Studies of an electrostatic air cleaning system.

The influence of the electrostatic forces on airborne particles have been known for centuries. These early discoveries have been summarized in several publications including the classical book "Electrostatic Precipitation" by White (1) and many others (e.g. 2, 3, 4). The utilization of the electrostatic force led to the development of electrostatic precipitator (ESP) which has been used for pollution control purposes since the beginning of this century. An excellent historical review about the development of electrostatic gas cleaning has been presented by White (1). When cleaning air from aerosol particles, electrostatic precipitator is a tempting alternative to mechanical filtration. This is mainly due to the relatively high removal efficiency and the low flow resistance of the ESP. Besides power plant applications ESP's are used in many other industrial applications. The same method is also used in smaller scale devices to clean air in office rooms, homes and restaurants. During the past decades several modifications of ESP's have been developed. This study focuses on an electrostatic air cleaning system developed by Ion Blast, Helsinki, Finland. The construction of this system is very simple and it has some similarities with the "wire in tube" electrostatic precipitator. However, instead of thin corona wire, a special corona electrode system is used to produce the necessary electric field and the unipolar air ionization. A typical feature of the Ion Blast system is the large diameter of collection tube - diameters up to 1 200 mm have been used in some installations. The large diameter requires that the corona voltage must be high. Ion Blast systems have been operated at the voltages up to 150 kV. The purpose of this study was to determine how the basic operational parameters, such as flow velocity, corona current and voltage, influence the performance of the Ion Blast system. Besides this, the aim was to clarify how the simple electrostatic theory could be applied when approximating the collection efficiency of Ion· Blast system in different operation conditions.