Improved modelling of solids friction factor for fluidized dense-phase pneumatic transport of fine powders using two layer flow theory
For the reliable design of fluidized dense-phase pneumatic conveying systems, it is essential to accurately model and scale-up important design parameters, such as the total pipeline pressure drop. The existing models for powder conveying in fluidized dense-phase mode are generally based on the data of limited number of products and pipelines and are found to be inaccurate under proper scale-up conditions. For the modeling of solid friction factor, a two-layer based model has been developed by separately considering the solids friction contributions of the non-suspension (dense) bed of powders flowing along the bottom of pipe and the suspension (dilute-phase flow) of particles occurring on top of the non-suspension layer. Volumetric loading ratio and dimensionless velocity have been used to model the non-suspension dune flow layer. Models developed using the straight-pipe conveying data of fly ash and ESP dust were validated for their scale-up accuracy by using them to predict the pressure drops in five larger and longer pipelines (69 mm I.D. x 168 m long; 105 mm I.D. x 168 m long; 69 mm I.D. x 554 m long pipes) and by comparing the experimental versus predicted pneumatic conveying characteristics. The two-layer model provided improved accuracy compared to existing models indicating that the model is able to better address the dense-to dilute-phase transition condition.