The mine is getting deeper every year – 30 m, according to industry reports.
As depth increases, so does the need for ventilation and cooling, and Howden knows this from experience working with the deepest mines in South Africa.
Howden was founded in 1854 by James Howden in Scotland as a marine engineering company and entered South Africa in the 1950s to serve the needs of the mining and power industries. By the 1960s, the company helped equip the country’s deep gold mines with all the ventilation and cooling systems needed to safely and efficiently extract ore miles underground.
“Initially, the mine only used ventilation as a cooling method, but as the mining depth increased, mechanical cooling was required to compensate for the growing heat load in the mine,” Teunes Wasserman, head of Howden’s Mine Cooling and Compressors division, told IM.
Many deep gold mines in South Africa have installed Freon™ centrifugal coolers above and below ground to provide the necessary cooling for underground personnel and equipment.
Despite the improvement in the status quo, the underground machine’s heat dissipation system proved problematic, as the machine’s cooling capacity was limited by temperature and the amount of exhaust air available, Wasserman said. At the same time, mine water quality caused severe fouling of the shell-and-tube heat exchangers used in these early centrifugal chillers.
To solve this problem, the mines began to pump cold air from the surface to the ground. While this increases the cooling capacity, the necessary infrastructure takes up space in the silo and the process is both energy and energy intensive.
To address these issues, mines want to maximize the amount of cold air brought to the ground through chilled water units.
This prompted Howden to introduce amino screw coolers in mines in South Africa, first in tandem after existing surface centrifugal coolers. This has led to a step change in the amount of coolant that can be supplied to these deep underground gold mines, resulting in a decrease in the average surface water temperature from 6-8°C to 1°C. The mine can use the same mine pipeline infrastructure, many of which are already installed, while significantly increasing the amount of cooling delivered to deeper layers.
Approximately 20 years after the introduction of the WRV 510, Howden, a leading market player in the field, developed the WRV 510, a large block screw compressor with a 510 mm rotor. It was one of the largest screw compressors on the market at the time and matched the chiller module size needed to cool those deep South African mines.
“This is a game changer because mines can install a single 10-12 MW chiller instead of a bunch of chillers,” Wasserman said. “Among the same time, ammonia as a green refrigerant is well suited for combinations of screw compressors and plate heat exchangers.”
Ammonia considerations were formalized in specifications and safety standards for ammonia for the mining industry, with Howden playing an important role in the design process. They have been updated and incorporated into South African law.
This success is evidenced by the installation of more than 350 MW of ammonia refrigeration capacity by South Africa’s mining industry, which is considered the largest in the world.
But Howden’s innovation in South Africa didn’t stop there: in 1985 the company added a surface ice machine to its growing range of mine coolers.
As surface and underground cooling options are maximized or deemed too expensive, mines are in need of a new cooling solution to further expand mining to deeper levels.
Howden installed its first ice making plant (example below) in 1985 at the EPM (East Rand Proprietary Mine) east of Johannesburg, which has a final total cooling capacity of around 40 MW and an ice capacity of 4320 t/h.
The basis of the operation is the formation of ice on the surface and transport it through the mine to an underground ice dam, where the water from the ice dam is then circulated in underground cooling stations or used as process water for drilling wells. The melted ice is then pumped back to the surface.
The main benefit of this icemaker system is the reduced pumping costs, which reduces the operating costs associated with surface chilled water systems by approximately 75-80%. It comes down to the inherent “cooling energy stored in the phase transitions of water,” Wasserman said, explaining that 1kg/s of ice has the same cooling capacity as 4.5-5kg/s of frozen water.
Due to the “superior positioning efficiency”, the underground dam can be maintained at 2-5°C to improve the thermal performance of the underground air-cooling station, again maximizing cooling capacity.
Another advantage of the particular relevance of an ice power plant in South Africa, a country known for its unstable power grid, is the system’s ability to be used as a heat storage method, where ice is created and accumulated in underground ice dams and during peak periods. .
The latter benefit has led to the development of an Eskom-supported industry partnership project under which Howden is investigating the use of ice makers to reduce peak electricity demand, with test cases at Mponeng and Moab Hotsong, the world’s deepest underground mines.
“We froze the dam at night (after hours) and used water and melted ice as a source of cooling for the mine during peak hours,” Wasserman explained. “The base cooling units are turned off during peak periods, which reduces the load on the grid.”
This led to the development of a turnkey ice machine at Mponeng, where Howden completed the work including civil, electrical and mechanical equipment for a 12 MW, 120 t/h ice machine.
Recent additions to Mponeng’s core cooling strategy include soft ice, surface chilled water, surface air coolers (BACs) and an underground cooling system. the presence in mine waters of elevated concentrations of dissolved salts and chlorides during work.
South Africa’s wealth of experience and focus on solutions, not just products, continues to transform refrigeration systems around the world, he says.
As Wasserman mentioned, as more and more mines go deeper and more space in mines, it’s easy to see solutions like this found in other parts of the world.
Meinhardt said: “Howden has been exporting its deep mine cooling technology to South Africa for decades. For example, we supplied mine cooling solutions for underground gold mines in Nevada back in the 1990s.
“An interesting technology used in some South African mines is the storage of thermal ice for load transfer – thermal energy is stored in large ice dams. Ice is produced during peak hours and used during peak hours,” he said. “Traditionally, refrigeration units are designed for a maximum ambient temperature that can reach three hours a day during the summer months. However, if you have the ability to store cooling energy, you can reduce that capacity.”
“If you have a plan with a fairly high peak rate and want to upgrade to cheaper rates during off-peak periods, these ice making solutions can make a strong business case,” he said. “The initial capital for the plant can offset lower operating costs.”
At the same time, BAC, which has been used in South African mines for decades, is gaining more and more global importance.
Compared to traditional BAC designs, the latest generation of BACs have higher thermal efficiency than their predecessors, lower mine air temperature limits and a smaller footprint. They also integrate a cooling-on-demand (CoD) module into the Howden Ventsim CONTROL platform, which automatically adjusts collar air temperature to match subsurface needs.
Over the past year, Howden has delivered three new generation BACs to customers in Brazil and Burkina Faso.
The company is also able to produce customized solutions for difficult operating conditions; a recent example is the ‘unique’ installation of BAC ammonia coolers for OZ Minerals at the Carrapateena mine in South Australia.
“Howden installed dry condensers with Howden ammonia compressors and closed loop dry air coolers in Australia in the absence of available water,” Wasserman said of the installation. “Given that this is a ‘dry’ installation and not open spray coolers installed in water systems, these coolers are designed for maximum efficiency.”
The company is currently testing an uptime monitoring solution for an 8 MW onshore BAC plant (pictured below) designed and built at the Yaramoko Fortuna Silver (formerly Roxgold) mine in Burkina Faso.
The system, controlled by the Howden plant in Johannesburg, allows the company to advise on potential efficiency improvements and maintenance to keep the plant operating at its optimum. The BAC unit at the Caraiba mining complex in Ero Copper, Brazil is also designed to use this feature.
The Total Mine Ventilation Solutions (TMVS) platform continues to build sustainable value-added relationships and the company will launch two Ventilation On Demand (VoD) feasibility studies in the country in 2021.
Right on the Zimbabwean border, the company is working on a project that will enable video-on-demand for automatic doors in underground mines, allowing them to open at varying intervals and provide just the right amount of cooling air depending on the specific needs of the vehicle.
This technology development, using existing available mining infrastructure and off-the-shelf data sources, will be an important part of Howden’s future products.
The Howden experience in South Africa: Learn how to design cooling solutions to deal with poor water quality at its deep gold mines, how to make solutions as energy efficient as possible to avoid grid problems, and how to meet some of the most stringent air quality requirements. temperature and occupational health requirements worldwide Regulation – will continue to pay off for mines around the world.
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