The throughput and efficiency of a SAG mill depends on the volumetric load: An overloaded mill has reduced coarse ore breakage, as the cascading balls and rock cannot drop far enough, reducing kinetic energy for breakage. An underloaded mill will break coarse ore well, but at the expense of added grinding ball consumption and increased risk of liner damage. Also, if underloaded, significant throughput will be lost in the fine and mid-size fractions as the surface area for attrition is reduced.
Typically, SAG mill control is performed with respect to bearing pressure and other process variables which are used to estimate volumetric loading in order to optimize the mill throughput. While these methods are typically effective, they can also have several shortcomings when changes in mill liners, lifter profiles (wear), ore density, rotational direction, and/or temperature occur. Using a highly innovative solution that is fixed in rotation with the shell of a SAG mill, MillScanner™ now provides the control room with a direct measurement of the charge toe location which can be used to optimize the mill. The accuracy of the charge toe / volumetric loading measurement will be independent of temperature, ore density, liner/lifter wear, or mill direction, and the result is an extremely consistent and robust process variable for use in control strategies that will both optimize throughput and increase mill reliability. In addition to providing the location of the charge toe, MillScanner™ also acts as an expert ear for the mill and has the ability to accurately detect ball-to-liner impact occurrences.
By quantifying the charge toe angle, or the media angle (βdynamic), on each rotation, a precise control strategy based on the internal dynamics and volumetric loading of a SAG mill is now possible. Also, by studying the complete evolution of the charge toe or media angle through the liner lifetime, improved strategies, liner designs, and control system performance is possible.
The included MillScanner™ PC software displays the radial vibrational trends to the control room for general supervision, and it will make the data available to any data historian, DCS/PLC, or Expert System via industry standard OPC communication.
The unit installs quickly and effortlessly to the mill using four liner bolts, and MillScanner’s™ wireless signal will travel up to 100 ft with a clear line of site to the receiver antenna.
MillScanner™ will provide valuable data to assist the mill operators in creating innovative strategies and improved liner designs to optimize throughput and increase reliability.
- Create optimal control strategies around charge toe and media angles as process variables
- Monitor liner wear and other efficiency changes in order to optimize liner/lifter replacement and design
- Improve grate discharge design to keep pulp level constant all through the mill length
- Optimize and control the mill media filling degree to reduce production costs while keeping the same grinding performance.