Two years ago, Ingeteam signed a collaboration agreement with the “Institute of Mining Engineering” (part of the University of British Columbia), for studying the effect of using variable-speed drives in grinding circuits. This agreement has been recently renewed for another two years.
The agreement is based on two different projects. The first, called “Variable Speed Drive Control System” builds off the two previous years of research on the use of variable speed control for grinding circuits applicable to one specific mine with ball and tower mills.
The preliminary results demonstrated the benefits from an operational perspective which are achieved with speed control, such as less energy consumption and increased throughput.
For ball mills, the mill’s speed can be adapted in response to changes in ore properties including hardness and feed particle size amongst others. This study also determined that as the mill’s liner wears, mill speed should be increased to maintain energy efficiency and grinding performance. For tower mills (VertiMill), mill speed was found to be a more responsive and accurate variable for controlling changes in hardness and throughput as compared to other more commonly used options such as changing the mill’s ball charge.
With this background knowledge, over the next two years the aim of the study is to develop a variable speed control system for the ball mill and the tower mill. The study will make it possible to estimate the costs of installing the variable speed drives and any additional instrumentation as well as the benefits to this specific case.
The second project, called “Operation Opportunities for Variable Speed Drives for HPGRs”, seeks to study the benefits of these systems based on the material’s properties and its effect on production rates. There is an increasing potential of High Pressure Grinding Rolls (HPGR).
HPGR systems have two counter-rotating cylindrical rolls with one roll in a fixed position while the other roll is allowed to float via a hydraulic piston.
In the case of HPGRs, the main operating controls are the specific pressing force and roll speed. Roll speed is controlled using a variable speed drive. The specific pressing force is defined as the force exerted across the cross-sectional area of the roll and is the primary mechanism for controlling product particle size and specific energy consumption.
The distance between rolls is referred to as the gap. The gap will dynamically adjust in order to maintain the correct specific pressing force between the rolls. The specific pressing force and roll speed, can be influenced by multiple parameters including moisture, feed size, ore hardness, roll dimensions, and operating gap.
The study will further investigate the differences between speed, throughput and energy consumption to better understand their inter-relationships in order to show how speed must be controlled in HPGR mills based on variations in ore properties (hardness, feed size) and how speed can be controlled to increase overall production in a comminuition circuit.
Over the next two years, a study will be conducted to assess the potential benefits of speed control for the HPGR to respond to ore variations and increase production, while reducing energy usage.
Iñaki Gorostiza | IMD Marketing Manager