Anglo American minimises coal dust exposure with foam

Workers at Anglo American’s Grasstree coking coal mine in Queensland benefit from a significantly lower level of dust exposure underground, thanks to an engineering system built in-house.

The purpose-built system reduces worker’s exposure to respirable coal dust by 96 per cent. It led Anglo American to winning the 2018 Innovation Award at the annual Queensland Mining Industry’s Health and Safety Conference (QMIHSC).

In tackling dust suppression, a continuous miner fleet is integrated with a bio-degradable foam solution, a material that is used for the first time in development mining.

As coal moves through mining machinery, the foam will bind to coal particles, suppressing dust exposure underground.

The system effectively reduces operators’ exposure to coal dust, a considerable amount of which is produced when the continuous miner is cutting coal.

While this dust is traditionally removed via a vent tube adjacent to the miner, a turbulent airflow caused by the rotating cutter head can allow coal dust to migrate to where the operators are standing at the back.

Anglo American’s site senior executive at Grasstree mine Tom Cobcroft says the company has a desire to achieve zero harm.

“Part of that journey from where we are today we have been able to implement some engineering solutions on our continuous miner fleet,” Cobcroft tells Safe to Work.

“And in this particular case it was a collaborative solution that was spearhead by the guys in development and the foaming system for dust control.”

In conjunction with traditional dust mitigation strategies, poly integrated sprays are installed between the operator and the dust source on the non-vent tube side of the continuous miner.

It sprays at an angle of 60 degrees, allowing the dust in-bye side of the poly apron spray to be captured in the air that flows towards the vent tube.

Further, the team has also fitted an enviromist spray system that runs at a high pressure to the miner.

The spray targets respirable dust in the 2.5 to 20 microns range; sprays positioned on the boom of the cutter head in the throat of the miner spray the conveyor, while the ones placed on the tail of the miner spray down on the shuttle car.

But a problem remains even after fitting the two systems. Dust was still being generated when the coal was transferred between the mine conveyor and the shuttle car en route to the vent tube.

These systems represent short-term solutions to reducing dust exposure, but they did not satisfy the team’s ultimate goal – to find a solution that would further reduce dust exposure.

“The problem we have with the coal dust is all the coals sitting in front of the shovel as it gets loaded out,” Anglo American’s development superintendent Wayne Barnes says.

“It has to come back through over the guys and back to the ventilation system.”

After testing multiple different solutions, the Grasstree development team applied a foam product to the flychain in front and behind the hydraulic tank, where most dust is generated and can be eliminated at its source.

The team then put up a foam rate of 10 litres per minute while the miner is in the bolting system.

Given the foam’s thick consistency, it can slowly run down the chain and onto the shovel. This movement smothers the coal on the chain and the shovel in front of the miner.

But the team found out that this rate can be further increased to 20 litres per minute to keep up with the chain run during the production cycle and deliver additional benefits.

Based on the monitoring data collected before and after the foam dust suppression system was installed, the difference was “immediate and significant.”

Development maintenance trade supervisor Gareth White says, “We designed a few prototypes for the foam system, so we could figure out the best way to deliver the system and how the product will react with the coal.

“So once we got some good results with that, we designed a more compact, a more miners-friendly system, which is what we have now.”

As the foam system delivers significant health improvements for the Grasstree underground workers, it reimagines working underground and creates safe zones that isolate workers from dust sources.

The system is being applied to other pieces of Grasstree’s plant underground, in particular the breaker feeder at the belt transfer point.

It is also being implemented at Anglo American’s other underground operations and shared with its industry peers.

This article also appears in the January-March edition of Safe to Work.