Electrical control of electrostatic precipitation

Abstract

Considering electrical control of electrostatic precipitation, this paper discusses particle collection in terms of corona ionic wind, gas flow pattern and high-voltage power sources. Experiments and simulations were conducted with lab-scale and industrial electrostatic precipitators. In general, a larger electrostatic precipitator (ESP) index value leads to better ESP performance. To maintain the voltage, simulation results show that a three-phase power source could operate at a lower ripple factor of 0.8% and a shorter recovery time of 5 ms after spark-over than single-phase or high frequency transformer rectifiers. For an industrial ESP with several electric fields, optimal voltage or electric field strength drops from its inlet to outlet fields. It is normally around 3.3 kV cm−1 with a large corona input power for the inlet field, and it drops to about 2.3 kV cm−1 with a small input power to limit ionic wind induced reentrainment for the last field. For a typical Chinese 660 MW coal-fired boiler with a four-field colder-side ESP, its outlet ash concentration and its PM10 and PM2.5 are usually around 15 mg m−3, 12 mg m−3 and 2 mg m−3, respectively. According to particle image velocimetry observation and particle collection measurements, we found that the corona wind generated vortex can result in not only enhancement of collection but also particle reentrainment and/or the so-called ‘bypass flow’. An optimum electric field inside the ESP exists to save energy and collect particles. For present ESPs, a higher electric field (>3.5 kV cm−1) generates strong electrohydrodynamic flow, which consequently undermines the collection due to turbulent flow. Advanced industrial automatic voltage controllers for three-phase transformer rectifier and double-wire ESPs have been developed according to those experimental results for both reducing emission and corona energy consumption.