High efficiency gas treatment using bi-directional pulse power system

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The characteristics of high efficiency gas treatment system by bidirectional pulse corona discharge were investigated.The NOx removal efficiencies were measured using either bidirectional or unidirectional pulse discharges. The width of bidirectional pulse was 100 ns for each positive and successive negative voltage pulse. The NO and the NOx removal rates increase with applied voltage for any voltage waveform. In the case of the pulses of 200 ns for 5 Hz and the pulse of 100 ns for 10 Hz, the NO and the NOx removal rates of 88.6% and 84.5% are obtained for the unidirectional voltage of 100ns. However, these for the bidirectional pulse are the lowest. The reason, why the removal rate for the bi-directional pulse is low, is considered that the input energy for the bidirectional pulse is lower than that for the unidirectional pulse. Therefore, the removal rates as functions of input energy are investigated. As a result, the NO and the NOx removal rates increase with increasing input energy. The removal efficiency for unidirectional pulse of 100 ns is superior to that for the pulse of 200 ns. The removal efficiencies for the bidirectional voltage pulse of 200 ns and that for the unidirectional pulse of 200 ns are on the similar curve.Also, framing photographs of discharge were taken by using high-speed camera. It is thought that all pulses equally remove NOx up to 100 ns. After 100 ns, the corona discharge is occurring only near the inner electrode in the case of the bidirectional pulse and the unidirectional pulse of 200 ns. Therefore, the energy efficiency is not high. It is found that the best way is to finish the application of voltage before streamers reach the outer electrode and to prevent the generation of corona discharge limited to the vicinity of the inner electrode.