MechChem Africa January-February 2022

⎪ Heating, cooling, ventilation and air conditioning ⎪

“Every kW of electricity that is consumed underground – by equipment, lights, or vehicles – also converts di rect ly into heat, which typically adds up to several megawatts of heat. All this heat has to be removed, either by chilled air sent down from the surface, and/or by chilled water produced underground or pumped from surface and delivered to underground air coolers,” Potgieter explains. “Having built an accurate 3D model of the mine, VUMA-Network first does an air flow solution. Then, by adding the heat specifications to VUMA for all con- tributors and the working locations, we will get a clear idea of the ventilation and refrigeration requirements necessary to meet the mine’s needs. We can then run various scenarios involving different ven- tilation and refrigeration technology op- tions to find an optimum solution that will offer the mine the best value for money in terms of energy efficiency and capital investment,” he informs MechChem Africa. Potgieter explains the two broad op- tions open to ventilation and refrigeration engineers for maintaining a healthy air flow and temperature: “As air descends into a mine the temperature increases due to auto-compression, significantly reducing the potential cooling capability of the ambient intake air; to such an extent that in ultra-deep mines in South Africa, ambient intake air adds to the mine’s heat load. In these scenarios, circulated air must be kept to a minimum with mechani - cal air cooling from chilled water and/or ice being used to cool the underground environment. “For mines of up to 1 500 m, large scale bulk air coolers on the surface, typically producing 400 to 500 m 3 /s of chilled air at 10 to 12 °C, are used to provide cooling, with powerful fans exhausting the chilled air through the mine.

“Chilled water can also be used as service water for drilling, dust suppression, clean- ing and other underground maintenance tasks, while still contributing to offsetting the heat load,” notes Potgieter, adding that VUMA software is able to optimise the ventilation and chilled water balance very accurately and quickly between all available options. “There are a lot of other variables apart from depth that need to be considered, though. For mines making use of diesel equipment, chilled water may be needed at much shallower depths due to the heat given off by machinery. Mines in Ghana mining at depths of less than 600 m rely on big surface coolers that provide up to 14 MW of air cooling due to the massive heat loads associated with the under- ground machinery, and the elevated ambi- ent temperature in central Africa on the surface, which can be as high as 27 °C wet bulb,” Potgieter informs MechChem Africa. Hattingh continues: “Ventilation and refrigeration are among the most costly operational expenses on a deep mine, so minimising the energy required becomes a critical aspect of mine design. There is, therefore, growing interest in the use of electric vehicles underground, because of their potential energy savings and emis- sions performance. “Mines also tend to be extensive and subject to constant change. They have a magnitude of branches that affect the flow of air getting to where it is needed. VUMA gives users the reliable answers they need to accurately optimise air and heat flow – to within a degree. And best of all, the software is free, not only for mine developers but also to help mine operators manage their ventilation and refrigeration resources on an ongoing basis,” he adds. “For new mines, we can plan for the life-of-mine operation and consider initial,

build up and ultimate requirements, while for operating mines, the software can identify how to best respond to changes. Mine managers are routinely shutting down depleted workfaces and opening up new areas in search of profitable ore bodies. This changes the air and heat flow paths. BBE’s VUMA-network simulations can accurately determine the effects of these changes and how to optimise and manage changes to the system,” Hattingh explains. Other software capabilities include: • Transient modelling: “Mining compa- nies value their workforce and take great care to ensure work is carried out as safely as possible. To achieve this, mine management establishes evacuation procedures in the event of a total power failure. VUMA can quickly determine the time it would take for the temperature to rise to dangerous levels,” explains Potgieter. • Underground f ires: VUMA is able to simulate where the gases would go, the concentrations of smoke and the temperatures in different areas of a mine. • When designing a ventilation system, all airborne contaminants must be considered, such as, flammable gases, dust, vehicle exhaust fumes and a host of other potential dangers on a mine. Factors related to these haz- ards are built into VUMA as design criteria to address associated risks. VUMA gives our clients a clear view of actual and potential underground venti- lation and cooling requirements and how best to meet these needs. The product is free, and we at BBE are available to add our expertise to implement any new needs that VUMA predicts are necessary,” Hattingh concludes. www.vuma3d.com

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