Modeling Solids Friction for Dense-Phase Pneumatic Conveying of Powders

Abstract

This article results from an ongoing investigation aimed at developing a new validated test-design procedure for the accurate prediction of pressure drop for dense-phase pneumatic conveying of powders. Models for combined pressure drop coefficient (''K'') for solids-gas mixture were derived using the concept of ''suspension density'' by using the steady-state ''straight pipe'' pressure drop data between two different tapping locations of the same pipe and also for two different diameter pipes. It was observed that the derived models were different depending on the location of tapping points (for the same pipe) and selected pipe diameters. The derived models were then evaluated by predicting the pressure drop for pipelines with various diameters or lengths (69 mm I.D. Â 168 m, 105 mm I.D. Â 168 m, 69 mm I.D. Â 554 m) for the conveying of power station fly ash. A comparison between the predicted pneumatic conveying characteristics (PCC) and the experimental plots showed that the models resulted in significant over-predictions. In the second part of the article, the ''system'' approach of scaleup was evaluated. ''Total'' pipeline pressure drop characteristics for test-rig pipelines were scaled up to predict the PCC for larger=longer pipes. It was found that the ''system'' approach generally resulted in grossly inaccurate predictions. It was concluded that further studies are needed for a better understanding of the solids-gas flow mechanism under dense-phase conditions.

Energy loss at bends in the pneumatic conveying of fly ash

“…It has been considered that Barth (1958) expression would be valid for dense-phase mode, whereas it is believed that the Barth (1958) model was originally proposed for coarse particles in dilute-phase flow. However, several researchers such as Pan (1992), Pan and Wypych (1998) and Mallick (2010) have used this model for fine powders conveying in dense-phase. Hence, this model has been evaluated for the fluidized dense-phase conveying of fine powders in the present paper.…”

“…It is to be noted that the equation (2) includes the (∆p z ) solids term. Therefore, there liability of Schuchart (1968) bend model would depend on the accuracy of modelling solids friction through straight pipes, which in itself is an area of active research (Mallick, 2010).…”

“…This model does not take into account particle properties, location of bends, etc. The value of bend loss factor (accounting for the radius of curvature of bends) has been considered as 0.5 (Mallick, 2010). The air density and velocity have been considered corresponding to the bend outlet conditions.…”

“…The air density and velocity have been considered corresponding to the bend outlet conditions. Considering the popularity of this model (Mallick, 2010), the same has been evaluated in the present study.…”

“…However, modelling of solids friction factor ( ) on its own is a matter of active research (Mallick, 2010). As the prediction of bend loss depends on the value of calculated ∆p z (in turn on the estimated value of λ s ), hence any limitation in modelling solids friction factor would also affect the predicted value of bend loss.…”