Howden recently worked with a North American hard rock mine to introduce a Ventilation on Demand system using VentSim™ CONTROL technology bringing dramatic benefits in safety, energy costs and reduced carbon footprint.
The mine was sunk to extract high-grade copper ore from a deep deposit. It is designed to produce around one million tonnes of ore per year. From the start, environmental protection was a major factor in planning and operating the mine workings. In addition to the safety of personnel working underground, which is always the overriding factor, the operators were determined that the energy usage and carbon emissions from the project would be kept to the minimum required for personnel safety and comfort.
One of the largest operational cost drivers in underground mines is the ventilation system. Traditionally, mine ventilation fans have been run continuously even when not needed. In the case of this mine, there is a total of approximately 18,000 HP of fans installed, 50% being underground auxiliary fans and 50% main surface fans. The task for Howden was to introduce a management and control system that used these fans effectively to ensure safe ventilation levels throughout the mine while reducing the power consumption to the minimum.
A unique control strategy was implemented to minimise the overall resistance in the mine and optimise the speed of the main fans. This was reckoned to offer the best balance between energy savings and smooth control response. The speed of the main fans is governed by the actions of the main ventilation regulator, through a mechanism known as a 'speed optimizer'. The auxiliary fans are equipped with on/off starters. Different levels of control are used to control the auxiliary fans, 'scheduling' and 'VOD', used in parallel to optimise their use. In the 'scheduling' mode, the fans are started and stopped at the beginning and end of the shift in the relevant zone of the mine. The 'VOD' mode is enabled at the start of the shift and uses the data provided by the electronic vehicle and personnel tags. This leads into high energy savings for both the auxiliary and main fans.
The mine has around 90 auxiliary fans on the site, all were fitted with scheduling control, and about half of them also currently have dynamic control strategy. These fans are switched on when there are vehicle movements or personnel working in the area, and switched off after the area is once again empty of people.
In calculating the savings achieved by the introduction of VentSim™ CONTROL Ventilation on Demand (VOD), we investigated the way the ventilation system would otherwise have operated. In the case of the auxiliary fans, a base case was first established, to estimate how much power would be consumed by each fan if no VOD system was available. We looked at the records over a 96 day period and scaled the figures up to one year. This demonstrated a reduction, over the twelve month period, of 15,000 MWh, which at the prevailing energy costs brought a saving of $1,200,000.
Additional savings arose from running the main surface fans in 'speed optimiser' mode, and decreasing the fan's speed for around 1.5 hours at the end of each shift. Comparing electricity consumption with figures from a previous period showed that the annual energy saving in the main fans was about 9,500 MWh. The cumulative cost
saving was calculated to be around $1,700,000. Savings in energy costs thus totalling $2,900,000.
Further benefits are that the mine has the flexibility to draw more air where required, maximising production and responding quickly to any adverse conditions; such as extreme cold or hot weather, power outage, communication loss, or anything else that may arise. In addition, the system optimises production by minimising blast clearing times, which enable workers to get back to work more quickly. Such control would not have been possible without the use of the advanced control system of the VentSim™ CONTROL system. While these benefits bring great economic advantages to the system, the wider value of the VentSim™ CONTROL VOD system, in reducing both costs and carbon footprint, is clear.
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