Estimation of particle size distributions in mineral process systems using acoustic techniques

[摘要] ENGLISH ABSTRACT:A desire to increase the efficiency of the comminution process in mineral process systemshas led to the need of determining the size distribution of ore particles at various stagesin the system. The objective of this research is to investigate the feasibility of the use ofan acoustic sensor for measuring particle size distribution. The acoustic signal generatedwhen the particles impact on a cantilever bar is analysed using digital signal processingtechniques. As rocks fall onto a metal bar, the bar vibrates. The vibrations containinformation th a t is extracted to determine the size of particles tha t impacted on the bar.The bar is modelled as a linear system which is excited by impulses (impact of particles).The response of the bar is deconvolved from the acoustic signal to obtain an impulsewhose amplitude is proportional to the energy of the impact. In order to improve sizeestimates, deconvolution is performed using a statistical model of the impulse sequence(Bernoulli-Gaussian) and then estimated using MAP estimation.Size estimates are not only a function of the mass of particles, but also on the exactposition of impact on the bar. Since there is always a variation in the position of impact,size estimates are erroneous. It was found that the position of impact can be determinedas to reduce variances dramatically. Due to physical sampling in space, the sensor has abias towards larger particles. We show how this can be represented mathematically andremoved.This project is mainly concerned with rocks in the +8-25mm (+0,7-22 gram) size range.

[发布机构] Stellenbosch University