Auxiliary ventilation systems in mining and tunnelling: Air leakage prediction and system design to optimize the energy efficiency and operation costs

Abstract

The excavation of tunnels and mining roadways requires auxiliary ventilation systems to dilute the noxious gases from blasting and diesel engines and provide a safe environment for workers. Therefore, axial fans and ducting systems are generally installed to supply the required airflow rate to the working face. Due to the air leakage, the airflow rate varies along the ventilation duct and the design of the ventilation system is complex when leaky ducts are used. Thus, to ensure the required airflow rate at the working face, a proper sizing of the ducting system and auxiliary fan must be carried out. In this paper, analytical and CFD numerical models have been conducted to investigate auxiliary ventilation systems considering different qualities of the ventilation ducts. A forced duct of 0.6 m in diameter and 200 m long in a 14 m2 cross section mining roadway has been selected to predict the pressure drop and the air leakage along the duct. In addition, the power of the fan and the energy consumption have also been studied in the analytical models to optimize the energy efficiency and ventilation costs. The results obtained show that the power of the fan can be reduced by 74% if a duct 0.8 m in diameter is installed. Good agreements were obtained between the numerical approach and the analytical results. Finally, novel nomograms have been developed to design the ducting system and the auxiliary fans and estimate the energy consumption as a function of non-dimensional variables. Duct diameters between 600 and 2400 mm and tunnel lengths up to 4000 m can be selected to design the auxiliary ventilation circuits optimizing the operation costs.