Plasma-enhanced SO2 remediation in a humidified gas matrix: A potential strategy for the continued burning of high sulfur bunker fuel

Abstract

We report a substantial enhancement in the removal of gaseous SO2 by discharging a transient nanosecond pulsed plasma in a water vapor-saturated gas mixture. With the plasma alone (i.e., “dry”), the SO2 remediation is limited to approximately 15% reduction in SO2 (i.e., ΔSO2 = 65 ppm). In presence of water vapor, we observe 84% remediation (ΔSO2 = 500 ppm) during plasma discharge due to the availability of OH radicals. Here, there is a synergistic effect of adding water vapor to the gas mixture in which the plasma excites highly reactive OH radical species that drive a two-step reaction process: SO2 + OH → HSO3 and the subsequent reaction of HSO3 + OH → H2SO4, which precipitates out in the aqueous phase. The efficacy of this approach increases as we increase the temperature of the gas matrix, indicating the relatively low barriers of this reaction, which is consistent with the OH-driven reaction pathway, and it also increases with plasma density, thus demonstrating the scalability of this approach. Plasma emission spectroscopy as well as Raman scattering spectroscopy provide spectroscopic evidence of the OH radical species, further substantiating the OH reaction intermediate mechanism. This approach provides a promising mitigation strategy for the continued use of high sulfur fuels (i.e., bunker fuel).