Methodology for the Estimation of Sphericity of Fiber and Hull Shaped Biomass Particles

C.A. Moreno-Chaves; D.C. Guío-Pérez^*; S.L. Rincón-Prat
Universidad Nacional de Colombia, Department of Mechanical and Mechatronics Engineering

Research group on Biomass and Optimization of Thermal Processes (BIOT)

Carrera 30 N° 45 A 03; Bogotá D.C - Colombia

*(0057 1) 3165000 Ext. 11207, dcguiop@unal.edu.co

Abstract

Estimation of particles sphericity is a critical issue when aiming to model or predict the behavior of a fluidized bed. Accurate techniques for the determination of sphericity, such as micro-tomography and laser scanning are expensive, time-consuming, and therefore not available for routine measurements. Image analysis is in turn more accessible, but accurate only in cases where the particles have a high sphericity [1]. Natural materials such as residual biomass suppose a great challenge on this regard given the variety of shapes and the shape differences between size fractions [2,3,4]. The present work proposes a methodology for the estimation of sphericity of selected biomass particles (rice husk, oil palm fiber and oil palm rachis). Ideal models based on the approximate geometrical shape of particles (cylinders for fibers and flat flakes with constant width for hulls) were deduced, and different shape factors were calculated and tested on its ability to correlate experimental measurements with the ideal proposed shapes. For the selected materials, perimeter, projected area and length were measured through image analysis; additional width measurements were performed for hull-shaped particles. Focus variation microscopy was performed to measure the particles surface and volume, and to determine their actual sphericity. Experimental data were used to find the most suitable ideal shape and shape factor that describe the actual shape of the selected particles, these relations were then used to predict the sphericity. Results showed that diameter to length ratio could be used to predict the sphericity of fiber-like particles, while width to perimeter ratio and Sympatec sphericity parameter can be used to predict the sphericity of hull-like particles. The findings strengthen the potential of image analysis together with the ideal geometrical models for sphericity estimation, since they indicate that once an accurate model is adjusted to the particles shape, simple 2D image analysis can accurately be used to predict sphericity.

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