Comparison of positive and negative DC discharge under coal pyrolysis gas media at high temperatures

Abstract

To study the characteristics of positive and negative DC discharge under coal pyrolysis gas media at 20 °C–600 °C, the IV characteristics and the current composition are analyzed under different conditions. Due to the difference of ionization mechanism, the corona onset voltage of negative corona is lower than that of positive corona under air gas medium. Under non-electronegative gas media, no corona occurs during negative discharge. However, during positive discharge, with the increase of output voltage, three types of discharge are successively observed, namely corona, glow and arc. Under N2 gas media and at 400 °C, the maximum collection efficiency of positive electrostatic precipitator is 98%, while that of negative electrostatic precipitator is 82%. When the collection efficiency is 70%, the energy consumption index of negative electrostatic precipitator is about 200 times higher than that of positive electrostatic precipitator. A linear relationship between I/V and V is observed and the ionic mobility can be calculated through the slope. At 350 °C, the ionic mobility under H2 gas medium is 5.25 cm2/(V*s) while the ionic mobility under N2 gas medium is 0.1 cm2/(V*s). The ionic mobility is proportional to the absolute temperature according to the discharge experimental data at 350 °C–600 °C. The factor βi, which is only related to gas media, is 0.0001653 cm2/(V*s*T) for N2 and 0.0087308 cm2/(V*s*T) for H2. These results assist in understanding the property of ESP at high temperatures.