An Australian mine site has been operating apron feeders for the past two decades. To increase efficiency and reduce downtime, the site's management contracted HYDAC to replace onsite apron feeder hydraulic power units (HPUs).

HYDAC Project Engineer Nick Blyth highlights that HYDAC's focus on condition monitoring and sensors in this application brought predictive maintenance to the fore, and with it "many returns on investment".

"The site in question has five dumping stations. We installed an apron feeder HPU on dumping station one in September last year and the apron feeder HPU to be fitted to dumping station three is likely to be installed in June, or July," Mr Blyth says.

What differentiates HYDAC apron feeder HPU?

Mr Blyth points out that the existing arrangement has two apron feeders powered by two individual HPUs.

"However, HYDAC is driving two separate individual apron feeders from a common HPU," he says.

"It's not a redundancy or a duty and standby pump. Rather they are both duty pumps that will be running all the time."

Advantages for the customer

Mr Blyth explains that combining them results in space savings in terms of having two power units versus a common power unit.

"The result is that electrical installation as well as monitoring of sensors and controls only has to take place for one power unit, which translates into big savings for the customer."

How does HYDAC's apron hydraulic power unit work?

The apron feeder hydraulic power unit drives a large hydraulic motor that's connected directly to the apron feeder. It predominantly operates in forward direction to feed out ore that's in the chute. It can also be operated in reverse if a blockage takes place at a reduced flow and pressure to prevent components from being damaged.

Mr Blyth adds that a noteworthy feature is proportional speed control.

"We've got feedback on the apron itself: we know how fast it's running. If the customer needs to speed up, we can proportionally give more flow from our power unit or slow it down to match the correct feed rate."

Electrical motor to drive the pump

A 250kW two-tonne electrical motor is used to drive each pump.

"Motors like this are custom-built and shipped over for these projects - they're not stocked at 250kW in Australia," Mr Blyth says.

Difference between HYDAC apron feeder hydraulic power units and previously supplied ones

The apron feeder hydraulic power units that were previously supplied to the mines had very limited options and scope for customisation, Mr Blyth points out.

All about condition monitoring

"It was just about ordering a power unit for that specific apron feeder size without much choice involved. The focus was not on condition monitoring and having sensors to monitor oil, temperature, oil pressure and flows.

"In comparison HYDAC's replacements have over 60 sensors in the unit. This means we can work with the customer and set up condition monitoring, and from that platform we can advise on maintenance intervals and when intervention is required to change pumps out - now that's real predictive maintenance."

 

Offline testing of pump

Another thing HYDAC executed - which is a first - was offline pump testing.

HYDAC isolated the hydraulic power unit from the apron feeder system and diverted the flow through a testing manifold and flow metres. This included a feature to artificially load the pump at different pressure settings.

Throughout this process HYDAC also executed data logging of the pump flows and case drain flows at different pressures.

"This data is benchmarked to monitor loss of pump efficiency, which can trigger a rebuild or replacement of the pump," Mr Blyth says.

"No other installed apron feeders have this level of functionality; it was something our customer really wanted, and we worked with them to come up with a solution they're happy with."

The pump has a maximum flow rate set by the customer at 960L/min and a maximum pressure of 350 bar.

Endurance operation order of day

Once installed the apron feeder operates 24/7 continuously for 20 weeks. At the end of this period, it has a three or four-day shutdown and then it returns to operation for a further 20 weeks. This duty cycle is set to continue for an anticipated lifecycle of 20 years.

Remote FAT

HYDAC executed apron feeder remote Factory Acceptance Testing (FAT) due to travel restrictions.

The test ran over a day for approximately seven hours.

"We had, depending on the time and what section we were testing, up to eight customer representatives in there.

"We ironed out a lot of the little bugs that we had on the first remote FATs. We also ran video feed - the main audio - of me doing the testing while streaming all the hydraulic power unit parameters that can be viewed on a separate screen.

"At the end, both feeds were converted into a video and sent for downloading."

HYDAC also upgraded the Wi-Fi connection to a dedicated wireless network to avoid loss of feed.

"Huge capability": remote FAT runs two 250kW motors

Mr Blyth points out that both 250kW motors were run for the apron feeder's remote FAT.

"To do that we run one motor off our generator and then we bring in a rental generator to run the other 250kW motor. That's a lot of installed power," he says.

He highlights that HYDAC can test up to 500kW of installed power within its factory according to current capability when executing a FAT. 

"That's a huge capability upgrade compared to the past!

"And then, the whole unit is broken down into modules for transport."

In conclusion Mr Blyth notes that practice makes perfect.

"We invested a long time to learn everything about the 750cc pumps, but after a while we were so familiar that it almost became an automatic task. All this effort has really strengthened the support capability we can offer the customer."