An evaluation of testing and modeling procedure for solids friction factor for fluidized dense-phase pneumatic conveying of fine powders

For the reliable design of a pneumatic conveying system, accurate estimation of solids friction factor through horizontal straight pipe is of paramount interest. Although the "straight pipe" method is fundamentally more appropriate, the "back calculation" approach provides several practical advantages for testing and modeling. However, earlier literature reports that "back calculation" approach suffers from 40 to 150% inaccuracy in prediction of total pipeline pressure drop in scale-up pipes, which had been discouraging for its use. In the present work, it has been argued that much of the criticism for the inaccuracy of back calculation method lies with the choice of its format of modeling solids friction factor. In this paper, "back calculation" method of modeling has been used by employing a "two layer" model format for solid friction factor for fly ash, ESP dust and cement. These models, when scaled up to predict the total pipeline pressure drop in larger and longer pipelines, have resulted in overall deviation from experimental data ranging from 3 to 35%, which is a significant improvement in prediction capability. The results prove that the selection of a better format of model for solids friction factor could significantly improve the reliability of "back calculation" method.