The high-pressure grinding roll (HPGR) system is typically more energy efficient compared to the crushing and grinding process because HPGR relies on particle-to-particle compression rather than impact and abrasion. In the CEEC report, the HPGR process is mentioned as one that was deliberately developed to enhance energy efficiency in comminution processes, especially for ores with higher hardness. Consequently, in most cases, the HPGR system is adopted when the intention is to minimize the electricity energy needed for ore preparation before processing in downstream mills.
HPGRs are known to generate finer particle sizes and more even particle size distributions, as well as generating micro cracks within the particle structure. This reduces the amount of energy needed for grinding operations in subsequent stages. According to the CEEC paper, conventional crushers and tumbling mills tend to load materials randomly and variably, while HPGR uses a consistent compression zone for effective breakage. It is, therefore, common practice to insert HPGR before ball mills to reduce grinding requirements or to substitute some of the grinding duties performed by SAG/ball mill circuits.
While there is no clear indication of how much energy savings can be achieved, some numbers are provided in the literature cited in the CEEC paper. Typically, savings of between 10 and 20 percent when compared to SAG-based circuits have been observed. In some closed-circuit HPGR operations, over 50 percent reductions have been observed in some cases. For the Cerro Verde Copper Project, the HPGR-ball mill circuit was calculated to use 15.9 kWh per tonne compared to 20.1 kWh per tonne in the SABC circuit, an appreciable reduction in energy consumption. Similar results were reported for the Los Bronces circuit.
Furthermore, HPGR may offer better performance than conventional crushing because the product it produces is partially “prepared” for grinding. As noted in the paper, the very high levels of compression exerted by the process result in micro-cracking, which can improve grindability, decrease the Bond ball mill work index, as well as circulating loads, thereby improving ball mill capacity. In turn, this lowers the energy consumed per tonne of mineral even if some additional energy consumption occurs due to HPGR.
At the same time, HPGR cannot always be considered more energy efficient than crushing due to the fact that the efficiency of HPGR is highly dependent on the type of ore used in the process. It is stated in the literature review that moisture, feed material characteristics, roll pressure, and the circuit itself influence HPGR efficiency. Moreover, additional auxiliary equipment needed for HPGR operation has to be taken into consideration when evaluating energy and capital requirements.
In summary, from all the proven data, HPGR is more energy-efficient than conventional crushing circuits, particularly in hard rocks, as well as circuits where microcracks and fine feed into mills can be effectively utilized. One of the main advantages is that it does not simply have low energy costs in crushing operations; rather, its greatest strength is that it reduces the overall energy requirements in the circuit, since grinding becomes less expensive.
