Ion density-enhanced electrostatic precipitation using high voltage nanosecond pulses

This study evaluates the beneficial effects of discharging nanosecond pulse transient plasma (NPTP) in a coaxial electrostatic precipitator for capturing nanoscale soot particles (similar to 50 nm) produced by an ethylene flame. Here, the nanoscale soot particles are collected using two different reactor geometries: a 3 '' diameter reactor with a mean flow velocity of 1.2 m s(-1) and a 1.5 '' diameter reactor with a mean flow velocity 1.5 m s(-1), corresponding to volumetric flow rates of 11.5 CFM and 3.6 CFM, respectively. The nanosecond high voltage pulses (+20 kV, 20 ns, 800 Hz) are applied in conjunction with DC bias voltages. While nearly 100% collection efficiency can be achieved without NPTP at sufficiently high DC voltages (|V-DC| > 14 kV), this drops below 50% for lower DC voltages (|V-DC| < 10 kV). With NPTP, we observe substantially enhanced remediation (up to 23x) at lower DC voltages (|V-DC| < 10 kV) due to the enhanced ion density produced by the plasma. For DC-only electrostatic precipitation, the charging of soot particles takes place via a DC corona, whose ion density is several orders of magnitude lower than that of the NPTP, which produces a streamer discharge due to the fast rise times of the nanosecond pulses (i.e., dV/dt similar to 10(12) V s(-1)). High speed imaging of the plasma emission profile indicates that ion densities 10(6) times higher are achieved with the nanosecond pulsed plasma, as compared to that of the DC corona. At lower DC voltages (i.e., |V-DC| < 10 kV), the charging of soot particles is a key factor limiting the DC-only remediation efficiencies, and NPTP provides a way to mitigate this limitation.