The Frick ammonia water chillers supply chilled water to a surface bulk air cooler (BAC) at a second ventilation shaft developed to service Bulyanhulu’s extended mining operations.
The installation, designed and constructed by ventilation, refrigeration and cooling specialist BBE Projects, will assist the mine to ensure continued safe working conditions.
“The chillers are a repeat order for the mine,” notes Johnson Controls operations manager Russell Hattingh.
The project is Phase II of a cooling solution specified by consulting engineering firm Hatch in 2010.
“The first phase saw the implementation of an identical plant system for 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,” explains Hattingh.
This project at West Shaft is a duplicate of the cooling system installed at 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.
BBE Projects director Richard Gundersen says that the second ventilation shaft was initially an up-cast shaft which 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 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 explains.
Phase III of this solution will see another pair of chillers installed to increase cooling capacity by another 7 Megawatts of Refrigeration ( MWr).
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 such that they could be manufactured off-site, broken down, containerised and then re-erected in the plant room with minimal on-site work,” says Hattingh.
BBE Projects were 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 JCI solution met these requirements, particularly in terms of efficiency and reliability. The Johnson Controls team also provide a good level of support,” says Gundersen.
“The chillers that Johnson Controls supplied were able to meet the technical challenges. It is a solution that BBE Projects and Bulyanhulu have used before, that has proven itself and can be trusted to perform in a remote, difficult-to-access location,” Hattingh concludes.