(402g) Theoretical Study of Granule Friability during Pneumatic Conveying

This work presents an improvement of methodology for predicting the friability of granules as an extension of our recent work [1]. The methodology of collecting experimental data of granule attrition using a laser diffraction particle size analyzer and the model combining CFD Eulerian gas-solid model with QMOM methodology for solution of particle breakage was developed and described in [1]. The combined model allowed us to relate the breakage kernel parameters to particular flow properties. It was found that for a given experimental set-up with diluted gas-solid flow, the breakage rate of granules is proportional to the characteristic particle size and to the square of the impact velocity between a granule and the equipment wall, and can be expressed using the form proposed by Moreno-Atanasio and Ghadiri [2]. Empirical parameters were evaluated by fitting the model to experimental data. The impact velocity was computed in [1, 2] using the CFD code as the solid-phase velocity magnitude in the cells next to the wall. Different components (normal vs. tangential) of the impact velocity vector are employed as in this work and results are compared with previous calculations. Theoretical simulations are also performed for (hypothetical) different curvature of the bend of the particle size analyzer. Simulation results indicate higher sensitivity of the breakage rate (1) to the bend curvature when employing the normal velocity or tangential velocity than for the velocity magnitude. As a conclusion we hypothesize that the velocity components are more relevant for quantification of the attrition and breakage during the dilute phase conveying of granules.

[1] P. Rajniak, K. Dhanasekharan, C. Sinka, N. MacPhail, R. Chern, S. Fitzpatrick, Modeling and measurement of granule attrition during pneumatic conveying in a laboratory scale system, In press, Powder Technology (2008).

[2] R. Moreno-Atanasio, M. Ghadiri, Mechanistic analysis and computer simulation of impact breakage of agglomerates: Effect of surface energy, Chem. Eng. Sci. 61 (2006) 2476 ? 2481.