High pressure water supply strategy for mine bulk air coolers
Abstract
South African gold mines face many challenges with rising production costs being amongst the biggest concerns. Labour unrest and low economic growth along with increased production costs are affecting the productivity and profitability of South African gold mines negatively. Therefore, it is of great importance that gold mines are as efficient as possible.
Gold mines in South Africa reach depths of up to 4 000 m. However, the gold grade has declined as high-grade gold deposits are close to being exhausted and mines are now exploiting deep-laying ore deposits. South African gold mines have large refrigeration systems, both on surface and underground, which is used to mitigate the effects of increasing virgin rock temperatures as mining activities become deeper each day. Therefore, the need exists to investigate strategies for improving underground cooling to ensure that workplaces are ventilated properly and environmental temperatures are below the legal requirement. This should be done without adding additional energy costs as energy tariffs are increasing continuously. High temperatures underground can be traced back to inconsistent water flow through centralised bulk air coolers (CBACs) because of the complex network of underground users. Improving the water flow will result in improved service delivery.
Research was done on different low energy cost systems for water reticulation/water cooling. Previous research mainly focused on energy saving initiatives, while only a few studies focused on obtaining service delivery improvements. Even though significant energy savings were achieved, some projects affected underground temperatures negatively. Therefore, scope was identified to utilise a high pressure u-tube system to supply production CBACs with the correct amount of chilled water to improve underground cooling conditions without adding additional pumping costs. No additional pumping will occur as the water will be transferred and displaced in the high pressure u-tube system and will not be pumped by the dewatering pumps. The strategy will increase the amount of chilled water through the CBACs to decrease mining ventilation temperatures and stope temperatures even when no mining activities occur.
This means that the air temperature will be improved throughout the day: even when no water is being consumed by the mining sector and while workers are making their way to/from workplaces.
The strategy was simulated and implemented at a South African gold mine. Chilled water flow through the CBAC was increased by 41.68 ℓ/s. The increased water flow decreased the outlet air temperature of the CBAC from 24.52 °C to 21.45 °C (daily average temperature reduction of 3.06 °C). This resulted in a 1 °C air temperature reduction at the development ends. The power consumption of the dewatering pumps decreased by an average of 2 322 kW per day, while the water-cooling power consumption increased by an average of 2 168 kW per day. Therefore, an energy reduction of 154 kW was achieved.
The study has been evaluated and validated which means that all study objectives has been met. Therefore, the proposed strategy can be implemented on all deep-level mines with suitable underground cooling configuration and CBACs. Potential benefits include improved settling, colder inlet water temperatures, and less contamination of the water.
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