Simulating breakage and hydro-mechanical dynamics in high pressure grinding rolls using the discrete element method

Other conference contribution, 2013

The compressive breakage principle utilized in a High Pressure Grinding Rolls (HPGR) is a highly energy efficient way of reducing the particle size of rock material, minerals and ores. However, there are a number of operational issues known related to the HPGRs. Due to the high forces and pressure levels acting upon the roller surface the wear rate is commonly severe contributing to a substantial part of the operational cost. It is also commonly difficult to achieve continuous optimal performance due to e.g. variations in feed material. Hence, there is a strong incentive to be able to model and simulate the internal behaviour in order to generate a deeper understanding, improve operation, solve problems and aid development of analytical models. In an HPGR both rolls rotates with a fixed speed. If a frequency drive is installed the speed is possible to change and control. The roll pressure is applied by fixing one of the rollers to the main frame and keeping the other roll in a floating condition with hydraulic actuators applying a force. This force is controlled by the start pressure level in the nitrogen accumulators acting on the hydraulic actuators. Roller position and the mechanical and hydraulic dynamic properties of the machine is complex since the response during crushing is both dependent on the hydraulic-/mechanical operational set points as well as the feed material response. In this paper the framework for modelling breakage as well as the dynamic response is developed. The rock material is modelled using the bonded particle model (BPM) approach. The breakage model is calibrated by conducting laboratory single particle breakage tests. The hydro-pneumatic system and dynamics are modelled using MSC Easy5 via a spring-dashpot system coupled to the DEM software which calculates a dynamic response in each simulation loop. Preliminary results indicate that the simulation framework can be used for investigating the complex relationships between feed material characteristics, operational conditions and the product output.