Mine ventilation, refrigeration and air-cooling installations provider BBE Projects has installed two new custom-built Frick ammonia water chillers at gold miner Acacia Mining’s Bulyanhulu gold mine’s West shaft, in the Shinyanga region of Tanzania.

The chillers were manufactured by technology group Johnson Controls and will supply chilled water to a surface bulk air cooler (BAC) at a second ventilation shaft developed to service Bulyanhulu’s extended mining operations.

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

“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 solution met these requirements, particularly in terms of efficiency and reliability. The Johnson Controls team also provides a good level of support,” states BBE Projects director Richard Gundersen.

Further, Johnson Controls operations manager Russell Hattingh says the chillers will assist the mine to ensure continued safe working conditions.

“The chillers are a repeat order for the mine. This project is the second phase of a cooling solution specified by consulting engineering firm Hatch in 2010. The first phase saw the implementation of an identical plant system for the 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 again now, complete the first cell of each of the two-cell BACs,” he explains.

Hattingh adds that the installed refrigeration capacity at both installations will double in the next few years.

Meanwhile, Gundersen explains that the mine’s second ventilation shaft was initially an up-cast shaft. However, it has, subsequently, been converted to a cold downcast shaft to accommodate Bulyanhulu’s extended operations.

He states that the chillers will allow for the delivery of cooled air to the working face 1 000 m 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,” Gundersen says.

Phase 3 of this solution will comprise the installation of another pair of chillers at the mine to increase cooling capacity by an additional 7 MW of refrigeration.

Gundersen points out that the chillers are custom-built ammonia units using screw compressors and plate-type heat exchangers.

Hattingh adds that the chillers comprise industrial designed Frick screw compressors, medium voltage motors, stainless steel plate and frame-type heat exchangers, piping, valves, instrumentation, electrics and controls.

He reveals that, to meet Hatch’s “stringent specifications”, the systems had to be modular such that they could be manufactured off site, broken down, containerised and then re-erected in the plant room with minimal on-site work.

“The chillers that Johnson Controls supplied were able to meet the technical challenges, and can be trusted to perform in a remote, difficult-to-access location,” Hattingh concludes.