MechChem Africa May-June 2024

⎪ Heating, cooling, ventilation and air conditioning ⎪

tification, and possibly correction, of sub standard conditions. But there are clearly risks, particularly at the design stage. This necessitates that rules are followed when the mine is in operation to ensure there is enough air for the development and stop ing. VoD systems would, by design, reduce the overall air requirement of the mine so it would not be possible to add additional production zones without impacting the air delivered to planned work zones. Good practices and procedures, and coordination with ventilation and mining personnel, will however enable a safe and efficient system. A mine is not a static environment, continues Potgieter. Mining might start at one level, then move to the next level down. Mines are continually mixing the ore grades mined to optimise profitability, or close off mined out areas and open new production levels. Therefore, the ventila tion system would need to be adapted or upscaled quickly with instrumentation and supply infrastructure to enable the PLC to support any new production zone. So, the total capacity of the primary system really needs to take as many of these possibilities into account if value is to be maximised across a mine’s lifetime. An automated VoD system requires very careful design and there are no off-the shelf solutions, notes Hattingh. While standard

walking into an office.” However, while this is technically possible, VoD is nowhere near as easy to implement. While lights might not need to be on when nobody is in the room, underground ventilation can never be com pletely turned off without understanding the implications: re-entry, strata gas build up, availability of sufficient air, etc. “First and foremost miners have to have enough air to breathe, which is generally handled by bringing down a sufficient quan tity of the primary air from surface. But the air must also always be at the right quality. As well as removing impurities, the key air quality issues of a productive atmosphere at the work face are temperature and humid ity. Typically, we strive to maintain the air at each workface to a wet bulb temperature of 27 °C , with air pollutants below set Time Weighted Average (TWA) exposure rates.” The wet bulb temperature indicates the potential cooling capacity of the atmosphere and, combined with air movement, how effectively the evaporation of sweat cools down the human body. At wet bulb tempera tures in excess of ±32 °C, the risk of human cooling mechanisms failing becomes sig nificant, causing heat exhaustion and worse. Ventilation on demand is an existing practice in many mines where the risk of flammable gas presence is negligible. Shift overseers stop and start secondary fans, or choke ventilation ducting manually, to supply the required air volumes to work faces accord ing to activity requirements. Manual operation of VoD systems may not always be effective because it is time consuming and inaccurate, especially where multiple ventilation duct branch-offs are installed, which can result in over or under ventilating work faces. As a result, VoD is seen as part and parcel of mine-automation, not only to reduce electrical costs, but also to provide an optimum and reliable sup ply of ventilation to the right place at the right time to ensure safe and healthy work environments. Key to implementing an effective VoD solution is measurement. By knowing what the airflows, temperatures and humidities at each critical point in a mine are, it becomes possible to calculate the exact air velocities required for optimal working conditions. Using a VoD Controller (PLC), the data set from the whole mine, including the areas being worked at any particular time, can be analysed and used to continuously manage and optimise ventilation delivery. A further advantage of automated VoD systems is that live results may be visible in a control room on-surface, allowing the immediate iden Manual versus automatic VoD systems

control loops and routines can, and have been developed, implementation is not plug and play. A ventilation control system must be specifically designed and tailored to suit the intended application. This comes directly off the overall mining strategy and associated health and safety risks, which, along with the ventilation design require careful consideration. “At BBE, we have our VUMA Ventilation modelling software that can quickly be used to model and simulate ventilation for a mine design or extension,” Hattingh says. “Also, we have a spin-off product called VUMA Live, which can access live data from key areas to provide VoD control and a SCADA based overview showing how the ventila tion system is performing. This delivers the transparency to enable mine managers to make informed decisions on how to safely operate and optimise the system, and to predict what might happen when they make changes.” “If used properly, VoD can be a risk minimiser,” Potgieter concludes. The consequences of decisions become more exposed, while unintended consequences can be quickly identified and rectified. And while there are capital costs in volved in installing VoD systems, the safety assurance and life-of-mine cost savings that can be achieved make it worthwhile. www.bbe.co.za

VUMA Live can access live data from key areas to provide VoD control and a SCADA-based overview showing how the ventilation system is performing.

VUMA Ventilation modelling software that can quickly be used to model and simulate ventilation for a mine design or extension.

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