Removal of fine and ultrafine particles from air by microelectrostatic precipitation

Particles with dimensions less than 2.5 μm (PM2.5) have been identified as being potentially hazardous to human health. The electrostatic precipitation process, which is mainly used in industrial applications, displays a drop in the precipitation efficiency for particles in the range 0.1-1 μm. This paper is focused on the development of an impulsive microelectrostatic precipitation (μ-ESP) technology for indoor air cleaning applications. Short (microsecond) high-voltage impulses are used in this technology, which allows the magnitude of the electric field that particles experience to be increased without complete spark breakdown occurring and also reduces the energy consumption compared to that of dc-energized systems. The charging process of particles in the impulsive electric field used in the reactor has been analyzed. Ambient laboratory air and air-diluted cigarette smoke, which contain a significant proportion of PM2.5 particles, were used in the precipitation tests. In order to optimize performance for the μ-ESP process, different energization modes of the developed precipitation reactor were studied: dc energization, impulsive energization, and their combination. It has been shown that combined dc and impulsive energization of the two stage μ-ESP reactor produces the maximum precipitation effect. In both cases, ambient laboratory air and diluted smoke, 100% precipitation efficiency has been achieved for fine (250 nm and above) particles; in the tests with diluted smoke, a fine mesh filter was incorporated in the precipitation system to achieve this level of performance.