(152a) Solids Friction Power Law Variations and Their Influence on Pressure Losses in Fluidised Dense Phase Pneumatic Conveying

In dilute phase pneumatic conveying the particles are suspended in the carrier gas (usually dry air) with the frictional losses dominated by particle-wall and particle-particle collisions. In dense phase conveying, the particles are in contact with each other, with one of two distinct modes of flow occurring: plug/slug flow which is predominantly based on granular products and fluidised dense phase flow which is more suited to fine powders exhibiting good air retention capabilities. In dense phase-plug/slug flow, the resistance is dominated by the radial stresses that the moving slug applies to the wall of the pipeline. In fluidised dense phase flow the frictional losses are characterised by a mixture of particle-wall and particle-particle losses which are heavily influenced by the viscous behaviour of the gas-solid interactions.

Typically, an empirical based friction factor has been used to determine the associated frictional pressure losses in the fluidised dense phase pneumatic conveying. These friction factors are dominated by a power law relationship to the conveying air Froude number (Fr) and solids loading ratio (m*). For different materials, the exponents can vary significantly, which limits the application range of these power law models. This paper details the variation of the power law coefficient and exponents and their effect of these changes on pressure prediction. Also investigated is the application of utilising the flowability parameters of the Hausner Ratio and the permeability/de-aeration parameters in defining a generic fluidised dense phase friction model and the associated limitation due to the inherent sensitivity of the power law model.