With a continuing focus on critical minerals, Bulk Handling Technologies (BHT) has designed and manufactured a loss-in-weight feed system to control the mass feed rate of beta-spodumene at an expanding Western Australian lithium mine.
As part of a larger handling system designed and supplied by BHT to receive, store and feed beta-spodumene into the process, it was important that this very fine, abrasive and hot bulk material could be accurately fed into a mixer at a measured mass feed rate.
Due to beta-spodumene’s unique handling characteristics and the range of feed rates required, a loss-in-weight (LIW) system was deemed to be the most reliable option.
LIW feeders operate by constantly weighing the stored product in a small hopper and, using an integral controller, they measure the loss in weight over time as the product is discharged into the process. The rate of loss in weight determines the mass feed rate, and by continually adjusting the speed of the feeder (in this case, a screw feeder), the system will automatically maintain the target set point in tonnes per hour – despite variations in product bulk density.
Ready for difficult materials
BHT engineering manager Paul Ingleson said beta-spodumene can be a difficult bulk material to handle.
“Not only are we dealing with a hot product in this case, but beta-spodumene is well known for being extremely abrasive and for compacting and bridging in silos and hoppers,” he said.
For this reason, the LIW feeder hopper has been carefully designed based on material property testing results to achieve mass flow.
“The steep and rounded shape of the hopper reflects the poor flow characteristics of beta-spodumene,” Ingleson said.
“This hopper design will prevent hang-up and rat-holing and, when combined with a correctly designed feeder, will ensure uniform draw-down and ‘first-in, first-out’ performance.”
Another important consideration for any LIW feeder is how it is filled. As the hopper discharges the product over time, the hopper will eventually need to be re-filled. The typical rule of thumb is that the LIW feeder should measure the weight loss in ‘gravimetric’ mode 90 per cent of the time and then switch to ‘volumetric’ mode for 10 per cent to allow for a fast refill of the hopper.
“In this case, the same design principles were applied to the larger filling screw feeder and the main product storage bin to ensure reliable filling of the LIW Feeder hopper,” Ingleson said.
“The filling screw is much larger as it must deliver the product at a rate of more than ten times the LIW feeder discharge rate, but it must start and stop the flow reliably when required.”
Leveraging many years of experience in large screw feeder design, the engineers at BHT designed a custom feeder with abrasion-resistant materials, which would also ensure mass flow from the main bin. The filling screw incorporates a vent line above the outlet, which allows displaced air from the LIW feeder hopper to escape through a filter bag during filling, and also an emergency discharge outlet below the main storage bin to allow any product out of specification to be removed from the system.
Ready and available
Established in 2012 and offering extensive materials handling equipment and systems, BHT specialises in customised and innovative solutions.
With its custom bin and hopper design experience and extensive range of bulk materials handling feeding, conveying, and weighing solutions, BHT can offer complete packages to receive, store, and feed any bulk material reliably and accurately.
The company can also assist with site audits and troubleshooting and, where practical, provide refurbishment and upgrade options.