A novel control system for nitrogen dioxide removal and energy saving from an underground subway station

Abstract

The importance of indoor air quality in a subway system is growing rapidly because passengers' health and displeasure are interrelated. Among diverse indoor pollutants, nitrogen dioxide (NO2) emitted from automobiles may flow into a platform of underground subway through ventilation holes or stairs. The level of NO2 in an underground subway station should be managed to prevent its adverse effects because NO2 is harmful to health. In this study, a novel control system (self-control system) equipped with panel-type hybrid activated carbon beds were developed and applied to remove NO2 and save energy for ventilation from underground subway stations. To evaluate the removal efficiency by varying influential factors such as superficial gas velocity and relative humidity, we measured the NO2 concentration from diverse sampling points (ambient, platform, and before and after the hybrid activated carbon bed) before and after operating the self-control system. As a result, the NO2 concentration at the ventilation hole of the subway station (12.3-113.6 ppb) was higher than that at the air monitoring station (9.2-68.4 ppb, AIRKOREA operated by Ministry of Environment in Korea). The level of NO2 was changed by varying the relative humidity in ambient air. The removal efficiency of NO2 decreased from 66.3% to 60.5% and the pressure drop of hybrid activated carbon bed in the system increased from 2.2 mmAq to 5.4 mmAq when the superficial gas velocity (depending on inverter frequency) increased from 1.04 m/s to 1.82 m/s. Additionally, the removal efficiency of NO2 rapidly decreased with elapsed time and was affected by relative humidity and weather conditions. Finally, the level of NO2 in the platform was less than 50 ppb (which is the standard value recommended by the Ministry of Environment, Korea), when the hybrid activated carbon bed was set to 90 degrees (vertical direction on air flow). When the self-control system was operated in the heating ventilating, and air conditioning system of the underground subway station, the NO2 level in the platform was considerably controlled to below 50 ppb and the power consumption for ventilation reduced. (C) 2016 Elsevier Ltd. All rights reserved.