Discrete particle simulation of solid separation in a jigging device
thesisposted on 23.02.2017, 01:38 by Viduka, Stephen
This project presents a numerical study of solid separation in a jigging device, which is a high yield and high recovery gravity separation device widely used in ore processing. The mathematical model adopted is a combination of computational fluid dynamics (CFD) for the liquid flow and discrete element method (DEM) for particle motion. In the numerical model the motion of individual particles is 3 dimensional (3D) andthe flow of continuous liquid is 2 dimensional (2D), considering the bed thickness is 1/3rd of the bed width, and one CFD computational cell is used through the thickness. Periodic boundary conditions are applied on the front and rear walls to emulate a bed of larger thickness using a relatively small number of particles. The initial packing conditions consist of a binary-density particle system where the light particles and heavy particles, have respective densities of 2540 (glass) and 4630 (ceramic) kg/m3. There are 1130 particles each 1 cm in diameter. A comparison between numerical and physical experiments was conducted, and particle fluid interaction forces were examined. The importance of various particle fluid interaction forces were analysed in order to elucidate their influences on the bulkbehaviour of the particle system. The lubrication, Magnus, Saffman, virtual mass, and inertial forces are investigated, and quantitatively compared to the drag force which is assumed dominant in the system. Stratification is heavily dependent on fluid motion through the jig. The study explores 5 different pulsation profiles. The profiles studied include: sinusoidal, triangular, sawtooth-backward, sawtooth-forward, and trapezoidal. As an initial comparison, all simulations are conducted using a fixed peak-peak amplitude and pulsation period. Their relative performances are compared in terms of solid flow patterns, separation kinetics, energy, mean particle position, coordination number, and concentration profile. The underlying mechanisms are explained in terms of particle-fluid interaction force. These quantitative comparisons demonstrate significant differences in the segregation rate and energy used for various pulsation profiles. An extensive understanding is developed of internal processes in jigging. Further, a parametric study is conducted using variations in jigging cycle frequency and amplitude with particular consideration to boundaries of operation. Quantitative comparisons demonstrate significant differences in separation time, concentration mechanics, and energy consumption over varying parameters, and find different particle flow phenomena at the operational limits. This study has raised awareness for potential improvement and hence optimisation of jigging. Details of two separate methods to reduce segregation time and energy used per cycle are explained. Finally, given insight by means of the numerical model two original propositions are made for the future operation and design of jigs. These include an operational method of reducing energy consumption per jigging cycle. In addition to a novel jig design mechanically capable of executing an alternative optimum jigging profile.