Removal of dilute hydrogen sulfide gas in air on a large scale using wet-electrostatic precipitator system

The removal of H₂S gas in air stream on a large scale was demonstrated by the wet-electrostatic precipitator (Wet-ESP) system. The Wet-ESP system is composed of two-step treatments which are wet chemical process and electrostatic precipitation process. In the wet chemical process, H₂S gas was selectively neutralized by chemical reactions between H₂S and alkaline solution of NaOH or KOH at room temperature. As a result, dusts of solid salts such as Na₂S, K₂S and unreacted mist were emitted from the chemical reactor. Dusts were negatively charged up and collected by the corona discharge generated in the ESP reactor. The total flow rate of waste gas and the initial concentration of H₂S were fixed of 120 Nm³/hr and 600 ppmv, respectively. The removal efficiency of H₂S was proportional to the liquid-gas ratio and the gas residence time. The highest H₂S removal efficiency was achieved with KOH at the liquid-gas ratio of 4.94 and at the gas residence time of 0.504 sec. In the ESP reactor, high corona discharge power and long dust residence time were preferable to achieve low dust emission amount which was similar level with the atmosphere. It was achieved with the input power of 44 W and the dust residence time of 0.65 sec or with the input power of 124 W and the dust residence time of 0.163 sec. In the dust size measurement, it was found that the average size of exhausted dusts was relatively larger than those in the atmosphere. Although, the ESP reactor collected small dusts selectively at the lowest corona discharge power of 6 W, the emission of dust was linearly decreased in the whole range of particle size with increasing the corona discharge power. In addition, H₂S gas and dust from the dry system for sewage sludge were simultaneously removed by using a pilot scale Wet-ESP system. In this pilot system the total gas flow rate was 276 Nm³/hr. The av- rage initial concentration of H₂S and dust amount in exhaust gas from the dry system for sewage sludge were 21.7 ppmv and 21.87 mg/m³, respectively. In the pilot system, the removal efficiencies of H₂S and dust were 97% and 99% at 4.07 for liquid-gas ratio, at 1 sec for gas residence time, at 165.6 W for electric input power, and at 0.78 sec for dust residence time.