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New cooling system creates safer working conditions

8th July 2016

  

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The Bulyanhulu gold mine near Lake Victoria, in Tanzania, owned by gold miner Acacia Mining has installed two new custom-built Frick ammonia water chillers from heating, ventilating and air conditioning (HVAC) company Johnson Controls.

The chillers supply cooled water to a surface bulk air cooler (BAC) at a second ventilation shaft developed to service Bulyanhulu’s extended mining operations.

The extended mining operations at Bulyanhulu are taking place on both the reef 1 and reef 2 structures of the mine in areas where limited to no historic drill testing has been undertaken. This expansion hopes to add five-million ounces of high-grade mineable resources to the resource base in order to provide increased flexibility to mining operations and the potential to increase production in the medium to longer term.

The installation, designed and constructed by engineering consultant BBE Projects, will assist the mine in ensuring continued safe working conditions.

“The chillers are a repeat order for the mine. This project is Phase 2 of a cooling solution specified by consulting engineering firm Hatch in 2010. The first phase saw the implementation of an identical plant system for a BAC on Bulyanhulu’s main ventilation shaft. Each shaft requires two BAC cells and each BAC cell uses two chillers running in a lead-lag configuration. The pair of lead-lag ammonia water chillers supplied in 2010, and now, complete the first cell of each of the two-cell BACs,” notes Johnson Controls operations manager Russell Hattingh.

This project at the West shaft is a duplicate of the cooling system installed at the main shaft in 2010. Two chillers running in a lead-lag configuration supply cold water to one half of a BAC at each shaft. The installed refrigeration capacity at both installations will double in the next few years.

“This second ventilation shaft was initially an up-cast shaft. It has been converted to a cold downcast shaft to accommodate Bulyanhulu’s extended operations. The chillers allow us to deliver cooled air to the working face 1 000 meters below ground, where rock temperatures can reach 50 °C. The BAC uses water from the chillers on the surface to cool the air sent down the shaft to 8 °C. By the time the air reaches the mine workings it has warmed to 20 °C, which still provides sufficient cooling to allow operations to proceed. Phase 3 of this solution will see another pair of chillers installed to increase cooling capacity by another 7 MW of refrigeration,” explains BBE Projects director Richard Gundersen.

Hattingh notes that the chillers are custom-built ammonia units using screw compressors and plate-type heat exchangers.

“The chillers comprise industrial designed Frick screw compressors, medium-voltage motors, SMO plate- and frame-type heat exchangers, piping, valves, instrumentation, electrics and controls. To meet Hatch’s stringent specifications, the systems had to be modular so they could be manufactured off-site, broken down, containerised and then reassembled in the plant room with minimal on-site work,” he says.

Gundersen says BBE was responsible for the design, procurement and commissioning of the cooling system.

“The key design requirements for the chillers were reliability, consistent performance in a harsh environment and climate, cost containment in terms of power consumption and ease of maintenance. The Johnson Controls solution met these requirements, particularly in terms of efficiency and reliability. The Johnson Controls team also provides a good level of support,” Gundersen states.

Hattingh concludes that the chillers supplied by Johnson Controls were able to meet the technical challenges of the project. It is a solution that BBE and Bulyanhulu have used before that has been proven and can be trusted to perform in a remote, difficult-to-access location.

Edited by Tracy Hancock
Creamer Media Contributing Editor

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