SURFACE LOADING
In 2023 , Liebherr Mining achieved its first repower of a diesel-drive machine to electric drive , converting a R 9400 in Australia for Fortescue
Digging by design
Conversions to electric are becoming more common for hydraulic excavators , while remote control operation also remains a focus . GET solutions are also getting more advanced , reports Paul Moore
The mining excavator market is evolving – with more focus on electrification , and as part of that a lot of mines are looking at conversion , sometimes called repowers , as an option to reduce emissions from existing machines . Fortescue earlier this year delivered a prototype Offboard Power Unit to power a converted Liebherr electric R 9400 E excavator previously delivered to the Christmas Creek iron ore operation , part of the Chichester Hub . Trials of the machine using hydrogen fuel cell derived power have already begun .
The Liebherr R 9400 was originally supplied in 2010 as a diesel machine and was nearing the end of its operating life when Liebherr and Fortescue successfully retrofitted it to electric ( cable powered ) operation as the R 9400 E . This was Liebherr Mining ’ s first repower of a dieseldrive machine to electric drive and is also the first Liebherr electric excavator to operate in Australia .
The Offboard Power Unit is described in globally patent pending documents filed by Fortescue as follows : “ A power supply system is provided for supplying electrical power for operation of heavy equipment such as mining machinery , the power supply system having : a hydrogen fuel cell module for generating electrical power from stored hydrogen ; a power electronics circuit coupled to receive electrical power generated by the fuel cell module , and having at least one output for supplying electrical power generated by the fuel cell module to an external equipment load ; a battery module coupled to the power electronics circuit to allow charging of cells in the battery module using electrical power generated by the fuel cell module , and discharging of the battery cells through the at least one power electronics circuit output on demand .”
The document adds : “ Mining , particularly open-pit mining , uses large machines for efficiency of scale . In order to power such machines using non-polluting electricity can be challenging in view of the location , environment and mode of use of the machines . Embodiments of the present invention provide an offboard power unit ( OPU ) for supplying electrical power to operate heavy equipment such as a moveable mining machine . The power unit is designed to be mobile with the equipment being powered . Energy for the OPU is generated from stored hydrogen through use of hydrogen fuel cells ( HFCs ). By sourcing ‘ green ’ hydrogen ( eg hydrogen generated by electrolysis of water using sustainable electricity ), use of the OPU according to embodiments of the invention to power mining operations can be close to ‘ carbon neutral ’ insofar as neither the energy supplied nor its use in the mining site produces carbon pollution emissions .”
It adds : “ The trailing cable in use carries a substantial level of electrical current and / or high voltage between the OPU and the equipment , and should therefore be sufficiently robust and insulated as for use in a mining pit or similar . The trailing cable may have a length in the order of 300 metres , which allows the equipment a range of movement without needing to relocate the OPU . Since the equipment is typically mobile and
trails the cable behind it , there is preferably some kind of strong anchoring connection between the cable end and the equipment to prevent unintended disconnection physically or electrically . One way of anchoring is to wind an end portion of the cable around a circular structure that uses friction to maintain lock . The structure is connected to the equipment , but is able to pivot to allow a greater degree of freedom for movement . In addition or alternatively a cable reel of commercial variety may be included , either at the equipment end or the OPU end , for use in managing the length of cable deployed at a given time according to position and / or movement of the vehicle relative to the OPU . In consideration of magnetic flux that may be generated by current flowing through cable wound on the reel , it may be desirable to limit how many layers of cable can be wound on the reel . This is then determined by how large the reel is to accommodate more cable before needing to layer the cable on the drum .”
The document then adds : “ Different forms of electrically driven mining machinery may require significantly different electrical supply characteristics . For example , in terms of power requirements , the aforementioned DTH Drill ( eg Atlas Copco D65 ) may require electrical supply power in the order of 400 kW , a large platform drill rig ( eg Epiroc PV271 Blast Hole Drill with electric motor option ) may need around 700 kW supply , whereas even a small ( 250 t ) mining excavator ( eg Liebherr R 9250 E with electric motor option ) may require 1,000 kW or more in electrical supply power to operate . Moreover , some equipment needs direct current supply whilst others use alternating current . Supply voltage requirements can vary also , along with duty cycles .”
On scalability the description also states : “ The range of power requirements is addressed by embodiments of the invention by allowing each of the fuel cell , battery and electronics modules to be scalable and independently configurable in capacity . This flexibility in design of the offboard power unit provides opportunity to tailor sizing of battery and hydrogen fuel cells , in particular , to suit equipment applications . Hydrogen storage can also be tailored to suit equipment duty cycle and operational requirements .”
The R 9400 repower process
Back to Liebherr and the excavator conversion itself . “ Approximately 60 % of an electric-powered Liebherr mining excavator is the same as a diesel-driven machine , which helps to simplify the repowering process ” explained Chris Di-
28 International Mining | MARCH 2024