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South African mine ventilation specialist BBE, with 20 years of designing, commissioning, and troubleshooting critical ventilation systems in South Africa’s deep and hot gold, platinum and copper mines, is putting its experience to beneficial use across the globe, currently in Mexico, where mines are getting deeper. Director and Senior Engineer at BBE, Ross Wilson, explains.

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Ventilation and cooling in Mexicos minesMexico is a country with a long and rich mining history, and a mining industry currently experiencing a period of rapid growth. Exploration projects are discovering new and exciting ore bodies with the potential of sustaining future mining operations. Existing underground mines have been shallow relative to the deep and hot gold and platinum mines of South Africa, but this is changing as the shallower orebodies become mined out and mines start to exploit deeper areas.

What does it take to properly ventilate and cool a mine as exploration and maturation modify the variables? In Mexico, a land rich in silver, gold, zinc, and other valuable metals and minerals, mining rights owners are beginning to wrestle with these issues.

According to Ross Wilson, director and senior engineer at BBE, the landscape and environmental conditions in Mexico are different from those found in South Africa. With many of the deepest mines in the world, cooling and ventilation has, for decades, been indispensable to safe operations in South African mines. “It’s a non-negotiable consideration in every stage of the mine’s growth and lifecycle. However, in Mexico, mines are only just starting to grapple with the issue,” says Wilson.

Two recent projects by BBE in Mexico – one for a new mine and another for a mine reaching the end of its planned life – illustrate how different timelines, budgets, mine legacy issues and factors such as terrain impact successful design.

Feline agility? Super-compact, modular design

In the Mexican state of Chihuahua, a new underground silver, gold and zinc mine is being established. While the deepest ore can be found at the shallow depth of 500 m below surface, unusually hot ground water at temperatures of up to 55 °C is a challenge. BBE was asked to assist with the original mine design, and it was clear from the start that mine cooling would be required to provide acceptable underground temperatures.

However, the mountainous geography, remote site and short design life called for an innovative cooling system design. The 13-year design lifespan was far shorter than a typical South African cooling system and was the result of the rapid mechanised mining method used on the mine. The outcome was a modular design that is also one of the most compact in the mining industry.

“The BBE ventilation system design for the mine included two surface air cooling systems and three surface main fan stations,” notes Wilson. “We did the process design as well as the mechanical, civil, electrical and control engineering design. We aided with procurement and construction from a network of local Mexican suppliers, and we were on-site to assist with commissioning.” The project was implemented with the mine who managed the construction project.

“Given the constraints of the surface geography, both surface air cooling systems and surface fan stations had to be compact. The mine provided raised boreholes in locations that suited the underground mine, but not necessarily the reality on the surface. One air cooling system was on a ridge while the other in a valley. A modular approach was adopted to provide flexibility to accommodate the surface geography, save costs and minimise site construction time,” says Wilson.

Mining operations and cooling systems are often designed to last for 30 years or longer and are typically expensive bespoke designs that make extensive use of concrete structures and take a long time to construct. In recognition of the 13-year design life, the BBE design made extensive use of lighter weight prefabricated steel structures. This allowed the cooling system to be constructed rapidly. This approach will also allow a breakdown of the structure for reuse at different locations in future, contributing to the sustainability of the mine’s operations.

The air-cooling systems are designed to provide 4.5 MW of refrigeration duty and cool 200 m3/s of ambient air from 19.5 °C to 12.0 °C wet bulb. The system is efficient with a total absorbed electrical power of about 900 kW at the design duty. The main fan stations are dual axial fan systems with a total air flow of 240 m3/s at a total pressure of 1.8 kPa.

“While the cooling system will deliver the specified cooling capacity, the full benefits will only be realised with careful management of the underground ventilation system and control of the hot groundwater. This will remain an operating challenge for the mine,” adds Wilson.

Making an older mine profitable and safe

BBE also experienced a ventilation planning challenge at another project in Mexico, this time at a more mature mine.

The second cooling and ventilation project was a solution for a silver mine that commenced operations in the 1920s. A short-term solution was urgently needed to lower rising underground air temperatures and enable production to continue in deeper areas. The build was a brownfields site with many existing structures and constraints.

Wilson adds: “The challenges the mines face are not only related to depth and heat but also to inadequate ventilation planning. In shallow mines, ventilation is easy and can be achieved without careful ongoing planning and design. However, as mines develop and become deeper the underground ventilation systems, which include fans and ducts to direct air flow, need to be updated and to grow with the mine. An effective, efficient underground ventilation system could even eliminate the requirement for a cooling system altogether; but as a minimum, it is a precursor to the effective operation of any cooling system.”

BBE’s assessment indicated that a surface air cooling system and two large underground fans would be needed to lower rising underground air temperatures. For this project, BBE’s responsibility included the design, construction, and commissioning of the cooling system, including arranging shipping and delivery to site. A modular design, making extensive use of prefabricated steel structures, was again specified.

“We provided assistance throughout the project, including a full-time on-site supervisor responsible for quality, safety and schedule,” notes Wilson.

“If the life of the mine is extended to mine the existing deeper ore bodies, which is expected, the mine will need to design and construct a new ventilation and cooling system. BBE would welcome the opportunity to assist.” Key challenges faced by BBE on both projects were long lead times for delivery of equipment sourced from outside of Mexico: refrigeration machines, electrical equipment and underground fans. Local equipment suppliers and construction companies were found to be more cost effective with shorter lead times than international competitors.

“Mexico is an industrial powerhouse with an established professional mining industry, but the mines are starting to grapple with problems that South African mines have experienced for decades,” says Wilson. “Experience from South Africa cannot always be directly applied to another country, but experience can accelerate progress and we enjoy learning with our clients.”

“As Mexico’s mines get deeper and hotter, they will need to take a professional and conscientious approach to ventilation,” advises Wilson. “BBE is establishing itself in the region and hopes to help our Mexican clients to mine safely and profitably.”

www.bbe.co.za

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