By Eamonn Ryan | All photos by BBE Projects
A specialist in the design, engineering and construction of mine ventilation, refrigeration and cooling systems, BBE Projects is currently executing a turnkey project to design and construct a refrigeration plant and fan station at Northam Platinum’s Zondereinde No. 3 Shaft Project near Thabazimbi in Limpopo.
The project owner is platinum group metals miner Northam Platinum – implementing a major expansion drive that will see the construction of three new shafts on a block of ground on the Western Limb of the Bushveld Complex. Mine tunnels can extend some kilometres, and the two sections of the mine are separated by up to five kilometres. Conveying cooling from a refrigeration plant to the far mine workings over such distances becomes extremely inefficient from the perspective of air-cooling losses.
The expansion project has already seen the completion of the No. 3 Shaft barrel development at a depth of 1 380m, which will be equipped for personnel and materials handling, while another two shafts, still under construction, will handle ore and ventilation for the mine. The expansion is predicted to extend the mine’s lifespan by an additional 30 years.
Andrew Branch, director at BBE Projects, says the company was appointed to design and build the large surface refrigeration plant to chill service water and provide air cooling for the underground works, as well as an upcast fan station on the ventilation hole. “Ventilation and cooling form an integral part of the operational plan for Northam Platinum’s new block of ground. They would likely not be able to mine it economically without this new infrastructure,” Branch explains.
Branch further elaborates that BBE’s appointment to the project was based in part on the company’s long association with Northam Platinum, with BBE having provided consulting service to the mining house for many years, as well as being involved in the construction of several cooling systems at Zondereinde.
“Northam Platinum and their EPCM (Engineering, Procurement and Construction Management) contractor, felt comfortable trusting us with this project, given our track record, experience and specialist skills,” Branch says. “While the construction and technology used for this project are not unique, they are tried and trusted. Northam already has a large refrigeration plant on their existing No. 1 Shaft, and this new plant mimics that design.”
Branch advises that no significant challenges have been encountered during the project to date, adding that the company collaborated with the mine and the EPCM to identify any potential pinch points early and address them. For example, the long-lead refrigeration machine equipment, that was sourced from the US, was ordered early to give the Original Equipment Manufacturer (OEM) enough time to manufacture it, given global material shortages and a fragile supply chain.
BBE Consulting company started working with Northam on this project in 2018 with the pre-feasibility and feasibility work, then the front-end engineering and costing work for the mine through to late 2021, as part of the owner’s team.
“We worked closely with the EPCM on the mine design and specifying it as it relates to the ventilation requirements. We’ve consulted and constructed for Northam for close to 20 years, so it was a natural progression in late 2021 to be called in on the ventilation and cooling side of the new shafts, as part of the normal tender process for a large mining project. We were appointed in May 2022 on a lump sum turnkey basis for the full scope and signed the contract in August 2022.”
While the HVAC&R project value component is confidential, Branch says it is “[B]ig in our lives, the biggest contract BBE has ever had” and currently one of the biggest single build refrigeration system projects in the South African mining industry – at least for the last 10 years. “You’d have to look internationally to find a similar scale project,” he says. “We are doing a tailored design for the mine, drawing on all the industry norms and our experience to give them the right solutions,” says Branch.
The three-year project will see BBE install ten refrigeration machines into the surface refrigeration plant, which will ultimately have up to 70MW of cooling capacity, though Branch emphasises the project involves refrigeration more than ventilation – but the two go hand in hand in a mining environment. The company broke ground in October last year, starting with civil works for the major structures of the plant. This first phase of the project will be completed by November 2024, with work on the 12-month construction of the fan station set to start midyear this year. The second phase of the project will see additional work on the refrigeration plant, with final commissioning slated for mid-2027.
The ventilation and cooling requirements were laid out as part of the pre-feasibility, feasibility and front-end engineering work, evolving through several rounds of iteration as the mine design was refined. Branch lists the primary prerequisites of the HVAC&R element as: what is the required ventilation through the mine in cubic meters per second of air; and how many megawatts of cooling into the mine are required.
“From that we then determined the split between cooling in the form of cold water going underground and surface air cooling.” The detailed design specifications such as what pipes and switchgear, types of instruments are to be used, came out of the overarching project list of specifications that all contractors have to adhere to.
Branch explains that the chilled water is piped underground to the deep levels of the mine while the air is chilled on surface, then drawn down the material shaft and rock shaft to be redistributed underground. The cooling requirements for mine ventilation are determined by the life-of-mine design. There’s a wide range of factors that influence it: surface ambient conditions, the extent and depth of mining, divergent rock temperatures and other geotechnical factors as well as the mining method and plant mine production rates; the infrastructure for conveying the cooling, whether it is packed, ducted and insulated and whether it is returned.
He says in this particular application, there is not much opportunity to implement unorthodox energy efficiency measures, given the need for a high cooling delivery. “There are instances where one can use reject heat or geothermal heat for low-power absorption chillers – but this is not one of those cases.
“Service water that’s used in a mine is typically supplied underground as cold as possible, and then is returned to surface as hot as possible to extract all the cooling you can out of the water. That results in a need to bring that water temperature down quite a long way, for a large delta T between return and supply. Because the return water is hotter than ambient air, precooling towers are employed before the water goes into the refrigeration plant, which is an inexpensive cooling process. This evaporative cooling cost just consists of the price of fan power on the cooling tower.”
Pre-cooling provides another 14MW of almost-free cooling on top of the 70MW of installed refrigeration capacity. “We do a cooling design to be as efficient as possible by arranging the chillers to handle a large temperature difference and get the best result. Apart from that this plant has been designed to be robust and reliable, which is key for mining operations.”
The medium voltage switchgear is Actom, the programmable logic controller (PLC) and programmable automation controller (PAC) are ABB Freelance. The refrigeration system is based on York centrifugal packaged chillers using R-134a. This type of equipment was selected based on its proven performance and reliability and has become somewhat of an industry standard among South African mines.
He explains that Northam mine has an existing refrigeration plant built in the 90s to early 2000s that has these machines on them, so staff are familiar with the equipment and have a long-lasting relationship with the service providers.
Ultimately, there will be 10 of these refrigeration machines, which are being phased in – the first six in this current phase to be commissioned by the end of 2024, and the remaining four to be installed and commissioned by April 2027.
“The primary product is chilled water that’s used underground for hydropower equipment such as drills; as general service water; and as underground air coolers, be it bulk air coolers, open spray chambers, cooling coils or spot coolers. Some of the water is diverted to bulk air coolers, which will be a portion of about 9MW of the 70MW used for air cooling on surface. Heat rejection is through evaporative cooling towers, the large cell concrete structures which are designed for longevity and maintainability. Splash type fill, also something of a standard in the mining industry, is used because of its good resistance to fouling. The rest of the system is the standard steel piping, galvanised corrosion protected, and centrifugal pumps.
“The centrifugal modules are well-established equipment with a long service history in South Africa and are well supported with spares readily available. They’ve got standard open-drive motors, for which service and spares are again accessible.”
The switchgear and other equipment are in line with the project specifications. “We wouldn’t put something totally foreign down on the site, which complicates spares holdings, training and operations. We stick with the mine’s preferred vendor list for equipment,” he adds.
Elements of difficulty in meeting the design
As a greenfield project there are fewer constraints in terms of design and construction, Branch says. However, the main focus here is on longevity. “It is a brand-new shaft system on the mine, so a good life-of-mine with plant to last 50 years or so was the prerequisite. Another main challenge was the mine’s service water chemistry. The available service water supply comes from underground with all its dissolved salts and such. If you put that through chiller heat exchangers, the risk is of corrosion, so the heat exchanger tube material was a concern. We settled on using a copper nickel heat exchanger material, which is the de facto standard in the mining industry. Other exotic materials are available; however these come with a price tag that must be considered.
“The existing plant on the mine has that same spec and has had corrosion issues due to the aggressive service water – and a fair amount of maintenance has had to be done on the old machines over the years. We recognised this and so looked at other materials, in particular titanium to see if it’s worth the additional capital and operating costs. In the end the mine was happy from the cost-benefit analysis to stick with the copper nickel.”
The current state of the project is that there are some civil structures being erected, with work on the mechanicals starting later this year and the EC&I in early 2024.
As this project is ongoing, further vendors will only be appointed in the second half of the year at which time RACA Journal will do a follow up article on the equipment installation.