Study of ways of reducing energy consumption in a ventilation system

Abstract

For new mines with a large volume of excavation work and large loads at the face, most (up to 80%) of the methane is removed from the fragmented coal and newly exposed material in the course of mining operations. Studies of the dynamics of methane emission show that the quantity of air supplied to thin and remove methane may be reduced by a factor of 2-2.3 during offdays and unworked shifts. In connection with this, a significant savings of electric power can be realized (as will be demonstrated below) by developing regulable axial-flow ventilation fans that can be reversed during operation by rotation of the rotor vanes in order to regulate air flow by shift. The use of automatic control systems to start the synchronous electric motors of these fans would be an important additional means of energy conservation. From 10 to 15 tons of air is sent into a mine by a ventilation system for each ton of minerals extracted. The cost of the electric power used for ventilation now amounts to 20% of the total cost of mined coal. These figures will rise as mines are worked to greater depths and the cost of electric power increases. The amount of electric power consumed for ventilation is determined mainly by the amount of air required per unit of time (m3/sec) to safely thin and remove harmful impurities (methane, oxides of nitrogen and carbon, etc.) and by the aerodynamic resistance of the mine's ventilation system. These factors in turn depend on the length, cross section, configuration (topology) and type of support of the individual workings (aerodynamic resistance) and the efficiency of the main ventilation system (MVS) of the mine. The efficiency of the MVS is determined by the smile efficiency of the fans used for the specified productivity and pressure, the efficiency of the electric drive of the fans, and losses of energy (pressure, productivity -- leaks and air infiltration in the different elements of the ventilation system (calorifier, the inlet and outlet sections of the fans, diffusers, traps, plate dampers, rotating bends, etc.). Let us examine ways of reducing electric power consumption by influencing two of the three main factors that affect this characteristic: by regulating fan operating regime while the fan is operating; by automatically controlling the excitation of the synchronous motor of such fans. The required rate of air flow is determined as