Electrostatic precipitator for fine and ultrafine particle removal from indoor air environments

Abstract

An electrostatic precipitator was evaluated to reduce nanometric and micron-sized particles in indoor air environments. This process consists in a negative air ionizer assisted by a parallel-plate collector. The ionization stage contained four or eight corona needles, which were supplied by a negative high-voltage DC. The collection stage was designed in a plate-to-plate configuration, of which the plates are alternately connected to a high-voltage DC supply and the ground. Fractional efficiency (expressed in number) was investigated using NaCl ultrafine particles and atmospheric aerosol according to different geometric, environmental and operating parameters (concentration, relative humidity, collector and ionizer voltage, collector length, number of needles, and airflow rates). The results are discussed according to particle size. Under optimized conditions (eight needles, 20 cm collector length, −7 kV ionization voltage, 5 kV collection voltage, 1 m/s air velocity), the process revealed high performance levels. The efficiency of particles of 10–25 nm in diameter was 94%, between 30 and 300 nm the efficiency was 99%, while in the most penetrating particle size, the efficiency was 96%, with an ozone concentration at the outlet of the process less than 5 ppbv. This process generated a very low ozone concentration, which is an essential challenge for indoor air treatment. The results confirmed the existence of the partial charging regime for particles less than a few tens of nanometers for which the efficiency was lower. For these particles, the collection conditions (collection time and voltage) had no influence on the efficiency. For larger particles, both the parameters of the charging phase (ion concentration, charging time) and the parameters of the collection phase (collection time and voltage) had a significant influence on the collection efficiency.