Improved Parameterization of Fertilizer Particle Size Distribution

Abstract

Particle size distribution is an important physical property of granular fertilizers that influences their bulk behavior (e.g., packing and segregation). Several parameter systems for fertilizer particle size distributions are analyzed in this paper. The most common system used by the fertilizer industry is the SGN-UI system, where SGN is the size guide number (the median particle size) and UI is the uniformity index (the 10th percentile particle size expressed as a percentage of the 95th percentile particle size). This 2-parameter system, however, has many limitations. For example, it does not give a distribution function. Furthermore, the UI parameter does not accurately reflect the spread of particle sizes. It is therefore necessary to find a better parameterization system. Three size distribution functions (the log-normal, the Rosin-Rammler and the Gaudin-Schuhmann equations) were tested on a size distribution database composed of 377 samples from 7 fertilizer materials. Each function was fitted to the data by nonlinear regression. The Rosin-Rammler function is the best parameter system on the basis of an analysis of variance of the sum of squares of error from the nonlinear fits. Comparisons between the Rosin-Rammler and the SGN-UI parameters were also made. The Rosin-Rammler system is more accurate than the SGN-UI system, possesses the ability of prediction, and provides a measure of the goodness of fit. Therefore, the Rosin-Rammler system should be used to characterize size distribution of granular fertilizer materials instead of the SGN-UI system.