At our Mt Arthur Coal open-cut operation in the Hunter Valley in New South Wales, Australia, adherence to stringent environmental noise limits is essential. The mine is located close to residential areas of the nearby town of Muswellbrook. With the operation needing to increase production levels in response to customer demand, the noise limits could only be met with significant reductions in the operating noise of mining equipment. Mt Arthur Coal has collaborated with equipment manufacturer Liebherr to achieve the lower noise levels. New excavators and haul trucks – claimed to be the quietest of their type in the world – are now being delivered.
To meet its obligations to the Muswellbrook community, Mt Arthur Coal developed a noise specification that prescribes the maximum noise limits that can be emitted from mining equipment under a range of test conditions. This required excavators and haul trucks to become up to 15 dB(A) quieter in their noise emissions. At maximum attenuation, this equates to a 32-fold reduction in noise output from the machine. The ability of equipment to meet the requirements of the noise specification is a critical factor in the selection process.
Mt Arthur Coal formed a team to work closely with equipment supplier Liebherr to achieve the required noise level reductions. The project team utilised expertise from the production engineering departments of the manufacturer’s truck factory in Newport News, Virginia, USA, and their excavator factory in Colmar, France. The team also took advantage of Liebherr’s experience in the manufacture of noise suppression packages for smaller equipment designed to operate in inner-city areas of Europe.
The new excavators and haul trucks being supplied by Liebherr are designed to meet Mt Arthur Coal’s stringent noise standards. Importantly, they do so in a manner that minimises negative operational or performance effects. This has established a new benchmark for mining equipment noise levels, with the excavator and truck models being the quietest in their respective equipment classes.
Mt Arthur Coal has designed and constructed a noise test facility, the first of its kind in the world, to test equipment noise levels on a regular basis. The facility tests the majority of the operation’s mining equipment under a range of operating conditions in accordance with the site noise specification. All excavators and trucks are subject to a noise management program that is designed to ensure both new and existing equipment stays within accepted noise limits.
Testing is incorporated into equipment maintenance programs to ensure new equipment is complying with noise limits and that existing modified equipment is performing to design during the entire life of the machinery.
Meeting specified noise limits
Mt Arthur Coal’s noise limits are some of the most stringent of any operating mine in Australia. These limits are set by government and based on noise levels considered acceptable in the surrounding community. From noise modelling (prediction of impacts), Mt Arthur Coal has determined the maximum noise levels allowable from each type of equipment to achieve compliance against these limits. These equipment limits are specified in the site noise specification and relate to both stationary and dynamic test conditions that simulate the equipment working.
The specification was recently reviewed to reflect new learnings and achievements gained from the equipment attenuation process to date. This review resulted in lower noise limits being specified for new equipment and the introduction of a new ‘drive-by’ test as part of compliance acceptance. Ongoing compliance with the noise specification remains the primary responsibility of the equipment supplier.
The noise emission target for excavators was required by Mt Arthur Coal, under both stationary and operational test conditions, to simulate all phases of the digging cycle. Liebherr achieved 113 dB(A) under stationary conditions and 115 dB(A) when measured at one metre from the source under operational conditions, both of which are below the specification.
Each Liebherr haul truck was tested against the noise specification for overall sound power and frequency targets; while stationary, loaded, driven up a ramp under full power; and unloaded and driven down a 10 per cent ramp under retard. The overall sound power achieved the target of 113 dB(A) and complied with limits across all frequency ranges. The operator noise exposure was less than the target level of 75 dB(A).
Tim Haig, Mt Arthur Coal Open Cut Examiner, says, ‘The Liebherr trucks are so quiet that when I’m inspecting a shovel dig (operating) on shift, the first I hear is the Liebherr braking as it pulls right up to the shovel. With the Liebherrs, you can certainly see them long before hearing them’.
Bruce Folpp, the operation’s Mobile Equipment Maintenance Superintendent, agrees. ‘These trucks are so quiet, you can hardly hear one come into the workshop. This result has been achieved by factory involvement as opposed to retrofitting sound components to standard equipment’.
Technical details – excavators
The new R996 Liebherr Litronic excavators are fitted with sound suppression packages, designed as a series of suppression modules that work together to reduce the overall sound power of each machine. The sound attenuating devices include sound absorbing panels throughout the engine bay, under the deck area and inside the counterweight. Substantial enclosures, lined with further sound absorbing panels are placed around the power packs and the hydraulic cooler house. Access to these areas is available via modified catwalks and ladders.
Noise reduction from the engine fans is achieved by using multiple hydrostatically controlled units instead of a single belt-driven fan. The engine fans are also electronically speed controlled to provide cooling only when required, reducing noise emissions further. Exhaust system noise emission reduction is achieved using primary and secondary mufflers tuned to reduce engine output noise.
Technical details – haul trucks
The new T282 ultra class diesel electric haul trucks are assembled at Mt Arthur Coal with comprehensive sound suppression packages. The noise reduction features include an aerodynamically designed fan coupled with a larger capacity radiator, ensuring ample cooling capacity at lower fan speeds. Fan noise is further muted by a specially baffled grille, while still maintaining a similar profile to a conventional truck. Both the access stairway and the grille have been engineered to allow easy maintenance access. To reduce noise associated with retarding, a high-volume, low-noise radial fan delivers the cooling air to stainless steel ‘quiet’ grids. This reduces both grid blower noise and the electrical humming often associated with retard resistors.
The truck’s engine area is enclosed by a variety of baffles and enclosures. Fire-resistant blankets have also been installed for their acoustical properties and durability. Access to the engine area is provided through doors on each side of the engine bay and from below through double-opening belly pans. A reduction in exhaust noise is achieved by utilising specially designed mufflers. Chain mesh mud-flaps have also been installed, which absorb noise rather than reflecting it to the side of the trucks, helping meet the directionality requirements of the noise specification.
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