| Description |
Stoppings and other control devices used in underground mines can be viewed as air paths with high resistance. The amount of air that leaks through these devices depends on various factors including the type of construction materials used, workmanship, and stopping inspection and maintenance. Improperly constructed and poorly maintained structures will significantly lower this resistance and cause undue leakage. The circumstances of a real-world mine rarely exhibit the ideal conditions needed to obtain the most accurate measurements. The airflows and pressure drops in an underground mine are subject to considerable variation due to movement of equipment, opening of vent doors, and other changes. In addition, mine layouts are often extremely complex and may be such that the airflow profile at the location where a measurement is required is not fully developed. This can make it so that fluid-flow laws are not truly applicable. Nevertheless, a practical effort must be made. In ventilation planning, resistance values are often measured in the field or in an experimental lab. These measurements were used in a simulated model which was calibrated to match the field conditions. This calibrated model was then used to further evaluate the pressure/quantity requirements for future mining scenarios. Experimental tests conducted at the University of Utah's coal mine model indicate that for a set of similar stoppings, the trend of pressure drop across the stoppings decreases with distance from the main fan. The trend resembles an exponential decay curve more than a linear one. The resistance values measured in the lab are directly correlated to real world measurements by a physical scale factor of 1:625. A CFD model was calibrated to within 5% of the lab measurements. Additional analyses with the CFD model also indicated that with increasing distance from the fan, both pressure drop and leakage flow through the stoppings exhibit an exponential decay function. A single main fan system was compared with a system having a main fan plus a booster fan. The results indicate that the booster fan creates a substantial reduction in pressure drop across the stoppings and a reduction in leakage as well. A VNETPC model of a two-entry development section was used to further characterize leakage flow in terms of progressive mine development, building materials used, and engineering design strategies. From these analyses, a recommended method of prioritizing life of mine engineering designs and leakage reduction methods to be focused in the critical leakage areas was developed. These critical leakage areas are identified as a proportional distance from the main fan. This method is applicable to existing large or extensive mines as well as future projects. |
