Jong Won Choi

Developing effective, economical, and environmentally sound approaches for sewage sludge management remains an important global issue. In this paper, we propose a bioethanol-lignin (nonfood biomass)-based sewage sludge upgrading process for enhancing the heating value and reducing air pollutants of hybrid sewage sludge fuel (HSF) for the effective management of sewage sludge. Sewage sludge paste with the lignin-CaO solution implies drying at 105 °C accompanied by torrefaction at 250 °C. During torrefaction, moisture and partly volatile matter begin to evaporate, and are almost vaporized out to the surface. In this study, the proposed process enhances the net caloric value (NCV) to 37%. The lignin-embedded HSF shows a two-in-one combustion peak regardless of the mixing ratio, resulting in a 70% reduction of unburned carbon (UBC) emissions, which is one of the particular matter (PM) sources of combustion flue gas. Other air pollutants, such as CO, hydrocarbon, NO_x, and SO_x, were also reduced by the proposed process. In particular, SO_x emission remained at ~1 ppm (average value) regardless of the sulfur content of the fuel.

The electrospray is one of the most well-known spray techniques using highly concentrated free charges from high intensity electrical potential between two oppositely charged electrodes to produce very fine and highly charged water droplets in a conical shape (i.e., Taylor cone). We propose the application of this spray technology to a wet cyclone system to maximize particle collection efficiency. Highly charged droplets impact fine particles inside a flue gas, stick to the collector body, and fall through the cyclone cone in a gravitational direction. We have designed and fabricated an electrospray-driven wet cyclone electrostatic precipitator, investigating particle collection performance with a tangential velocity of similar to 10 m/s at the cyclone inlet, applying various voltages and water supply flow-rates. Experimental results show that the effective driving voltage for reaching the PM2.5 collection efficiency over 95 % is 35 kV. Comparing performances of previously commercialized wet scrubbers, in terms of the same treatment capacity, we obtained 70 % power and 75 % water consumption savings, respectively.