Permeability and diffusivity properties of bagasse stockpiles

The retention of fuel quality (heating value) and avoidance of spontaneous combustion are two critical issues in the large scale storage of bagasse. A computer model to predict degradation and heating in bagasse stockpiles has been developed at Queensland University of Technology (QUT). The acquisition of reliable experimental data relating to fluid flow through compacted bagasse is critical to the accuracy of this computer model as a predictive tool in the effective design and operation of bagasse stockpiles. Laboratory test equipment was designed to measure two bagasse properties that have significant effects on the oxidation (heating) and subsequent deterioration of bagasse during storage. Using this equipment, extensive measurements have been made of intrinsic permeability and diffusivity in both the longitudinal (parallel to bagasse compression) and transverse (perpendicular to bagasse compression) directions. It was shown that there is a close relationship between diffusivity and permeability for bagasse. This relationship is of significant interest as it enables accurate diffusivity data to be calculated using only permeability measurements. Permeability measurements can be undertaken more rapidly and with less equipment than diffusivity measurements. The results also imply that stockpiles can be highly two dimensional in terms of mass and energy transfer. Therefore improved predictions can be expected when using a two dimensional rather than a one dimensional stockpile model.