Improving air distribution in deep-level mine ventilation systems

Abstract

Improving underground mine conditions results in fewer ventilation-related fatalities and increases productivity. The objective of a subsurface ventilation system is to ensure sufficient quantity and quality of airflow in the working areas of a mine. Deep-level mines are typically overventilated with poor volumetric efficiencies due to old working leakage, deteriorated stopping leakage, air being recirculated and high fan pressures. Consequently, the low volumetric efficiencies are a direct result of poor air distribution. Additional air is distributed through these mines to compensate for the air used wrongfully. This practice consumes an unnecessary amount of electrical energy since more air than required is supplied to the system. Expensive electrical tariffs are the most significant contributor to mining expenses. Therefore, the management and sustainability of energy is the central focus of today’s mines. Any reduction in expenses increases the lifetime and production outcome of mines. Depending on the type of mine, underground mine ventilation systems can contribute up to 40% of the total electrical cost. The contribution of the quantity control devices can range from 20% to 70% whereas the contribution of quality control devices can range from 0% to 60%. The increasing depths, complexity, size and mechanisation of mines increase the ventilation demand, which influences the rising operational costs directly. At great depths, the ventilation cost and requirements will eventually be impossible to sustain. Mining expansion and high electrical tariffs are forcing the mining sector to reduce its operational costs while maintaining legal limits. However, the study confirmed a cubic relation between the power required to obtain a specific quantity airflow and the quantity itself (𝑃𝑜𝑤𝑒𝑟 ≈ (𝐹𝑙𝑜𝑤)³); therefore, a small reduction in airflow quantity can result in a large reduction of power. Literature was reviewed about the airflow quantity control (air distribution) of a mine ventilation system. A variety of strategies were considered in which improving the ventilation system allowed for the system to be more energy efficient. However, deep-level mine ventilation systems have a few constraints that young developing mines do not have. Old deep-level mines usually lack the newest and advanced monitoring and control devices presently available. The expected lifetimes of these mines are reducing rapidly, which limits the payback period to make long-term efficient system investments viable. Making advance modern improvement is, therefore, highly unlikely on deep-level mines due to the large changes required and the expenses involved. Consequently, deep-level mines usually have lower volumetric efficiencies than young developing mines. Thus, deep-level mines have a higher potential for reducing energy usage by improving the air distribution of the mine ventilation system. The objective of this dissertation was to create a feasible method for improving the air distribution of a deep-level mine ventilation system. The mine was considered as an integrated system in which small practical changes were made over the entire ventilation system. The ventilation changes had to be as cost-efficient as possible and remain within the mine’s operational standards. The study aimed to show that combining these small changes would have a large effect on the overall air distribution of the ventilation system. The improved system could then be considered for possible energy reductions and savings. A simulation-driven method was proposed since a simulation model is the most feasible way of considering a mine ventilation system as an integrated system. The method focused on creating, preparing and verifying a ventilation simulation model. Improvement predictions were implemented on the simulation model in a strategic order using four identification cycles. The first three identification cycles improved the air distribution from the surface to the working areas. The fourth identification cycle investigated the potential return improvements in the ventilation system. The simulation predictions enabled the researcher to analyse and investigate integrated behavioural changes on the overall ventilation system. A deep-level gold mine (Mine A), located near Carletonville, South Africa, was used as a case study for the methodology. The simulation model was calibrated to an average deviation of 9.27 kg/s. The model’s predictability was within an average deviation of 4 kg/s, which was considered acceptable for predicting improvement initiatives. The four identification cycle improvements were applied to the system. The primary ventilation system’s air distribution improved by 11%, which resulted in an overall volumetric efficiency of 78.3%. The average airflow of the working areas improved with a margin of 5 kg/s from the required airflow. This improvement was achieved despite an energy reduction initiative that resulted in the primary ventilation system being 8.4% underventilated. The improvement process reduced fan power by 1.4 MW, resulting in a R14.9 million saving within two years. Further improvement processes can still be investigated, and an unknown simulation prediction possibility can be considered for future studies.