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

摘要

The removal of HS 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, HS gas was selectively neutralized by chemical reactions between HS and alkaline solution of NaOH or KOH at room temperature. As a result, dusts of solid salts such as NaS, KS 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 HS were fixed of 120 Nm/hr and 600 ppmv, respectively. The removal efficiency of HS was proportional to the liquid-gas ratio and the gas residence time. The highest HS 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, HS 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 Nm/hr. The av- rage initial concentration of HS and dust amount in exhaust gas from the dry system for sewage sludge were 21.7 ppmv and 21.87 mg/m, respectively. In the pilot system, the removal efficiencies of HS 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.