ABB, the leading power and automation technology group, announced that it has signed a contract with Polysius Corporation USA for the Penasquito High Pressure Grinding Rolls (HPGR) extension project. The Penasquito property is located in the mining state of Zacatecas, in Mexico. Start- up of the HPGR project is scheduled for the fourth quarter of 2010.
ABB’s scope of supply comprises a medium voltage (MV) variable speed drive system that includes two motors, two transformers, and two MV ACS1000 water cooled converters for the high pressure grinding rolls. The drive system has a power of 2 x 2500kW.
HPGRs require drives systems with high dynamics and strong mechanical characteristics to sustain heavy loads and stress on the machinery. They can reach short term overload conditions up to 180% for 500ms. In steady state operation, while material is being fed into the rolls, torque oscillates between ± 20% around the nominal torque of 80%.
In addition, several factors influence the correct configuration of the drive system with particular attention paid to the impact of harmonics on the supply network, environmental conditions and the control interface.
In the mining industry, HPGRs frequently replace conventional semiautogenous (SAG) grinding mills, primarily to reduce energy consumption and costs within crushing and grinding circuits. They consist of a pair of counter rotating rolls, one fixed and the other one floating. The feed is introduced to the gap in between the rolls and is crushed. Variable speed drives can adjust the speed of the rotating rolls and thus the throughput of the units, which is advantageous for the grinding or crushing of inhomogeneous types of ore. As such, the grinding process can be optimised for ores with varying grinding properties.
HPGRs became commercially available in 1985 and were first used in the cement industry for the grinding of cement clinker; they reduced the energy consumption by up to 50%. This success paved the way for the HPGRs to be used subsequently with great success in the mining of diamonds in 1987, iron in 1994 and hard rock (copper, gold and platinum) in 2005 with improvement of the wear protection of the rolls.
ABB adds to the existing energy efficiency and productivity of HPGRs by optimising the grinding process with innovative variable speed drive systems. These drives further increase the HPGR’s throughput efficiency by up to 5%.