Another large Hunter Valley coal mine has started seriously tackling operational noise levels, continuing efforts by some parts of the industry to project a more community-friendly image of mining.

Contractor Thiess has commissioned five Hitachi EH4500-2 dump trucks fitted with new noise attenuation systems at the Mount Owen thermal/semi-soft coking coal mine, 20km north of Singleton in the Upper Hunter area. The trucks are said to meet demanding environmental noise emission conditions imposed by the New South Wales Government.

Xstrata-owned Mount Owen joins other major Hunter Valley mines such as Bengalla and Mt Arthur in modifying large trucks and excavators to reduce operational noise.

Equipment supplier Hitachi fitted its first Australian noise suppression systems in 2000 at Bengalla to a fleet of the 255-tonne-payload EH4500 trucks. Systems in use at Mount Owen were designed and manufactured in Brisbane by Hitachi Mining in association with mechanical consulting engineering firm, Chaseling McGiffin. According to Hitachi Mining general manager Peter Ross, the design of the Mount Owen noise attenuation packages drew on experiences from Bengalla and advanced the whole program to take account of improvements in noise control materials and truck design.

“Materials, methods and trucks designs have moved well forward since 2000,” he said. “The system fitted to Mt Owen’s trucks was extensively researched and engineered and includes a high level of sophistication and noise control to reach the target level of 113db.”

Foremost among the noise control measures are a redesign and realignment of the truck’s exhaust system and extensive attenuation around the engine area. The exhaust system has been changed from a single muffler to a system which includes a primary muffler for each cylinder bank, feeding into a common secondary muffler before exhausting into the atmosphere. Adequate clearance and air circulation for the mufflers and exhaust pipework was achieved through design changes to the truck body.

The engine bay is fully encapsulated with a sound-absorbing sandwich of acoustic insulation and perforated sheet metal. Engine bay access doors were treated with the same material.

The underbody of the truck, under the engine bay, is lined with acoustic panels, and attenuation panels were fitted to the engine firewall to absorb any noise coming over the engine. Similar acoustic panels have been used to line the high arch.

Rotating components outside the engine bay, such as hydraulic pumps, and all air induction tubes for the engine’s air cleaners, were insulated with sound attenuating material, while forward of the engine bay an attenuator compartment was designed and fitted to catch any upstream noise. Mounted on the front of the truck, the attenuator is fitted with a series of angled louvres to stop noise but allow unrestricted air flow into the engine bay for component cooling.

According to Ross, the attenuation package satisfied all environmental demands with only a marginal impact on truck performance – a result, he says, of the engineering expertise of Chaseling McGiffin.

“The trucks were designed to perform at particular levels and variations to their design could affect performance,” he said. “The noise attenuation system has integrated well into the basic design of the trucks and made virtually no change to their overall performance.”

At the Mt Arthur Coal mine, 5km south-west of Muswellbrook, operator BHP Billiton teamed with truck and excavator manufacturer/supplier Liebherr to reduce noise levels generated by its 327-tonne-payload T282 dump trucks and 650t R996 hydraulic excavators.

To reduce disturbance to nearby residents of Muswellbrook, BHPB worked with Liebherr to develop a noise specification prescribing maximum noise limits for mining equipment working under a range of test conditions. The guidelines required excavators and haul trucks to become up to 15 dB(A) quieter. At maximum attenuation, this equates to a 32-fold reduction in noise output from the machines.

A team formed by the mine owner and equipment supplier 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.

BHPB subsidiary Mt Arthur Coal also designed and built a noise test facility, the first of its kind in the world, to test equipment noise levels on a regular basis. The facility tests most of the site’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.

According to BHPB, 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,” BHPB said.

“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 1m 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% 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 lower than the target level of 75 dB(A).

According to BHPB, Mt Arthur has established a new benchmark for mining equipment noise levels, with the excavator and truck models being the “quietest in their respective equipment classes”