Engineering consultancy Bluhm Burton Engineering (BBE) has selected diversified technology provider Johnson Controls’ York YD dual centrifugal chiller for the cooling requirements for gold and copper producer Newmont Mining Corporation’s Subika underground project, at the Ahafo complex, in Ghana.

The chiller was selected for its efficiency, small footprint and proven reliability – a crucial requirement for mission-critical equipment in a harsh African environment.

The Subika project will expand the original openpit Ahafo gold mine into an underground operation, thereby extending the life of the mine. The underground mine provides access to higher-grade ore beneath the openpit. Having achieved first production in June 2017, Newmont expects to reach commercial production in the second half of 2018.

BBE was asked to assess and design a suitable ventilation and cooling system for the project.

BBE Projects GM Andrew Branch explains that, for the development in the current scope of works, BBE conducted a ventilation study and created a mine cooling concept design.

“We were then awarded a turnkey tender for the detailed design and supply of cooling equipment and, on investigation of possible refrigeration solutions, selected the YD chiller,” he says.
“We are familiar with Johnson Controls’ York chillers, having used them for a number of mining projects in Africa, where they have proven to be highly reliable,” Branch says.

He notes that, in this case, the YD dual centrifugal chiller meets the needs of the surface air cooling plant design – its 7 500 kW of cooling capability will get the water required for cooling to the right temperature, modulating cooling capacity and delivering significant efficiency over a wide operating range.
He adds that, with two compressors on one machine, it can deliver a substantial amount of cooling. The chiller is also ideal in terms of the phasing required, as another YD chiller will be implemented in a phased approach as capacity requirements increase.
Meanwhile, Johnson Controls engineering manager Russell Hattingh says the chiller uses two York centrifugal compressors operating in parallel and features a compact configuration providing many kilowatts of cooling.

“It is designed with advanced controls, ensuring enhanced reliability and operational efficiency, at full and partial load, delivering year-round energy savings,” he says, noting that the chiller will be built to specification for BBE, packaged and delivered on site, while a Johnson Controls team will install and commission the chiller.

During a company investor open day presentation in December, Newmont regional senior VP Alwyn Pretorius noted that the project, including the Ahafo mill expansion project, was advancing on schedule and within budget, and would extend profitable production to at least 2029.

He added: “[Subika] will also serve as the platform to explore and potentially extend the life of the Ahafo underground resource, which is one of [the company’s] best exploration prospects.”

According to Pretorius, Subika will mine 13-million tonnes over an 11-year life- of-mine. About 1.1-milion tonnes of ore a year will be mined from the underground operations. It is expected to produce 1.8-million ounces of gold over an 11-year mine life and features ore grades of 4.7 g/t.

The Subika underground mine is also expected to require development capital of $160-million to $200-million and to produce 150 000 oz to 200 000 oz of gold a year.