An automated safety system spanning 6.5 km, is incorporating programmable safety PLC technology to achieve integrated global and local control.
The safety network has been installed at the Antiene Coal unloader in the New South Wales’ Hunter Valley.
The safety system can respond to emergencies with a site-wide shutdown of machinery, and respond to local issues in remote sections of the long-haul conveyors.
The new unloader, off the main northern rail line, supplies Macquarie Generation’s Bayswater and Liddel Power stations, and has a capacity of 4000 tph over conveyors up to 5.5 km long.
Together the power stations supply power to around 40% of the State.
The $90 million contract to manage the system is managed by AbiGroup.
The unloader gives access to coal supplies that were previously unreachable, and will help ensure the continued viability of the power stations.
Coal is automatically unloaded into a dump hopper at the Antiene station, fitted with vibrating feeders.
A 220 m initial conveyor carries it up to the 5.5 km main conveyor to the power stations.
Emergency control
The system includes fire protection features.
“Fire is an issue on any materials handling system dealing with flammable materials,” Multiskilled principal engineer Doug Lithgow said.
“A lack of localised high-speed response can turn a minor inconvenience into a major disaster very quickly,” he said.
“If there is a fire, the system can immediately shut down that area of operation before the conveyors can carry the fire around the site,” he said.
Lithgow worked with Multiskilled system architect Brian Gordon to design and commission the project.
The system’s flexible design becomes important for localised response to safety issues.
Site-wide emergency stop functions are complemented by strong local area functionality, with responses to local issue programmed into the system.
It also facilitates high-speed simultaneous control of the drive motors needed at each end of the long conveyor.
Without simultaneous control of emergency stops, the conveyor belt could be split or the machinery damaged.
“We did have a kangaroo issue to consider, with kangaroos running out of the bush and bumping into the loader. This would trigger the emergency stop circuit,” Lithgow said.
“The tripped lanyard indication lights on the 5.5 km road alongside the long conveyor could be clearly seen from a vehicle, but we couldn’t see the lights on the side where the kangaroos were most likely to run out,” he said.
“People had to get out of the vehicle and go to that side to see if there was a problem.”
The control system helped solve this problem.
“The system enabled us to program the roadside lights to flicker at different frequencies, depending on which side there was a problem,” he said.
“This enabled us to clearly see where a problem was, while simply driving along the conveyor.”
Features
The Antiene system uses a single XPS MF3022 to govern 12 distributed control boxes, with a total of 240 input/output functions responding to particular areas and particular hazards.
The PLC provides dual redundancy fault detection, with dual port ram, dual processors and duality of all functions needed for the PLC to compare outputs and establish whether a fault has occurred.
The system operates through its own non-integrated safety circuit, with safety programming and hardware completely separate from standard automation functions.
This saves time and reduces operational complexity because the non-integrated safety functions do not have to be checked every time changes are made to standard automation features.
The XPS MF3022 manages 20 digital inputs and eight digital line control outputs with integrated two-port Ethernet switch, integrated SafeEthernet protocol (time deterministic Ethernet) , Modubus TCP/IP server and Modubus Serial (RTU) slave protocols.
The high-speed Ethernet system employed at Antiene uses high-speed single mode fibre for optimum response on the conveyor system’s far reaches, with multi mode fibre on shorter runs.
The PLC system provides a response time within 100 milliseconds from any point, and can be programmed to double that speed. Standard grade copper Ethernet cable enables users to connect safety PLCs and remote input/output modules, with a separation of 100 m between any two nodes.
The separation distance can be increased to over 80 km using fiber-optic cable. The open Ethernet system means users are not tied to a proprietary protocol, so operators can choose the best technology to integrate into their system.