Abstract

A comprehensive 3D simulation research of the stress formation on the microstructure level of hard rocks due to microwave irradiation applied in microwave assisted rock breakage is presented. The specific aim of the present work is to investigate the influence of microstructural details in inhomogeneous rocks. In order to use a realistic rock model, a two component 3D microstructure is generated. The two components are microwave absorbing and transparent, respectively. In the first step of the simulation chain the electric field inside the inhomogeneous rock is obtained by a 3D finite difference time domain (FDTD) calculation. In a subsequent thermo-mechanical finite element (FE) simulation the stresses generated by 15 s heating with 25 kW are obtained. High stresses on the boundaries of the microwave absorbing phase exceeding the tensile strength are observed. Finally, the numerical results are corroborated by microwave experiments performed on granite samples.

1 Introduction

Comminution is a highly energy consuming process where the energy efficiency is below 1% (Fuerstenau & Abouzeid 2002). In other words, almost the entire energy input provided for the process is wasted as heat and noise. A promising and powerful technique, which has the potential to significantly increase the fragmentation efficiency, is the prior microwave treatment of rocks followed by mechanical breakage operations. The aim of microwave irradiation is to pre-damage the rock (cracks, spallation) in order to weaken its mechanical properties. Microwave heating is driven by the absorption of microwave energy by the rock combined with the conversion of the electromagnetic energy into heat. The resulting inhomogeneous temperature field leads to stresses, which can exceed the material limit.

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