Dust Collector Installed at Train Bottom for Removing Particles in Subway Tunnel

Abstract

Many researchers have measured the dust concentration in subways around the world. The results have shown that harmful metal subway particles are distributed across subway platforms and inside passenger cars at a higher concentration than that found on typical city streets. Subway tunnels have been indicated as the cause of such noxious subway dust. Therefore, research must be conducted on the dust inside subway tunnel, and dust collectors must be developed to eliminate these particles. In this study, the properties of subway tunnel particle are measured, and a dust collector that can be attached to a subway train is developed and tested according to these measurements in order to eliminate dust inside subway tunnels. The daily change in tunnel dust concentration was measured twice at a temporary shelter located in the middle tunnel of Subway Line 5 in Seoul. The results showed differences in the impact of train operations and the open air according to the particle size. Particles 1 µm or larger did not move easily, and particles that were generated through train operations was usually 0.5 µm or larger. In the subway environment, the mass concentration of micron particles made up 90% of the entire sample. Therefore, in order to reduce the dust concentration in a subway environment, a dust collector that removes micron particles had to be designed. To survey the appropriate location for installing the attachable dust collector, the wind speed and particles concentration were measured for the trains bottom of Subway Line 5 in Seoul. The measurements showed that the wind speed in the lower area of the train on the outside of the rail was fastest, at about 50% of the train’s velocity. The dust concentration at the lower area at the top of the rail was also higher than that in the middle of the vehicle. The dust concentration at the bottom of the train was about 1.5 to 2 times higher than that measured inside the tunnel. Based on the bottom portion measurements, it was determined that the most effective installation point for the dust collector was on top of the middle rail of Car No. 4, which had an even train-induced wind and showed the highest dust concentration. The dust collector was developed on the basis of the aforementioned measurements. In an effort to consider the train-induced wind velocity of various subways, a hybrid dust collector combining an electrostatic precipitator and louver dust collector was devised. Each dust collector unit was designed to be optimized for subway particle through simulations and wind tunnel experiments. The louver dust collector was designed to be effective in collecting dust when the pressure drop is low. The electrostatic precipitator was designed to have a lower ozone emission rate when collection performance is high. Louver dust collector designs include an eight- and three-blade dust collectors with different pressure drops and dust collection efficiencies according to the number of blades. An electrostatic precipitator was designed to include a saw-type high-voltage electrode on a single-stage dust collector with a high processing flow. A hybrid dust collector that combined an eight-blade louver dust collector and electrostatic precipitator demonstrated distinct hybrid effects with strong collection efficiency, although but the inlet flow rate was low at only 0–2 m/s owing to the high pressure drop. For the hybrid dust collector combining a three-blade louver dust collector and electrostatic precipitator, only the efficiency of the electrostatic precipitator could be observed owing to the low collection efficiency of the three-blade louver dust collector. Upon predicting the amount of dust that would be collected by the two types of hybrid dust collectors based on the collection efficiency simulation results and particle concentration measurements, the side with the three-blade louver dust collector collected 23% more dust than the other side. Hence, the hybrid dust collector selected for attachment to an in-use subway train for experimentation was produced by combining a three-blade louver dust collector and electrostatic precipitator. Upon collecting dust from an in-use train, the louver dust collector collected approximately 1 g of subway dust after running for 10,000 km, whereas the electrostatic precipitator collected 164 g of subway dust. Because there was no change in collection performance during the 10,000 km test, the dust collector that was developed for this study was considered to have a refresh cycle of at least 10,000 km. Hybrid dust collector collected 50% of the dust weighed in the entire tunnel during 10,000 km running.