Assessing the energy efficiency of jaw crushers

It is well-known and taken for granted that the efficiency of energy use by comminution (i.e. breaking, crushing, grinding) equipment is very low, typically less than 10%. Most of the process input power is dissipated as heat and noise and ineffective deformation of the material to be processed and the device itself. Here, a study is reported that analyses the reasons for this low efficiency and tries to give recommendations for improvement. With a lab-scale jaw crusher as a test case, an optimisation was made on how to operate it most energy-efficiently by using an evolutionary algorithm numerical method. For a selected optimised case an attempt was made to simulate the jaw crusher using the EDEM® software for discrete element modelling (DEM), after first simulating single particle breakage using this software. Also, some experimental results on the crushing of several ~600 g pieces of rock while measuring electric power during the process will be reported. The results show that the physics of material strength readily points to theoretical maximum energy use efficiencies of around 15%, making it much more sensible to use this theoretical maximum as a reference point for efficiency improvement efforts. The experimenting was found to be well reproducible, showing little variation in crushed material size distribution when varying the crusher speed for a given crusher geometry. The DEM simulations were extremely time- and computing-power demanding while also the necessary input data on material properties were difficult or impossible to find. Nonetheless it was possible to produce simulation results that are representative of a real comminution process.