Development of high performance air purifying systems utilizing novel impeller-based liquid-gas mixing effect

Abstract

With the continuous development of industry, air pollution became among the most serious problems that the world faces. To resolve this matter, wet scrubber, which applies absorption method, is widely used in industrial fields. In fact, there still are drawbacks with current scrubber systems, and the technical development has been stagnated worldwide. Therefore, in this study, a novel scrubber system utilizing impeller-based liquid-gas mixing device was developed for the efficient removal for air pollutants. A sirocco fan-type impeller, a radial impeller, was equipped with mesh sheet for the generation of micro-sized liquid particles. With this particular impeller, liquid particles with about 70 µm of diameter were generated, which can highly enhance the liquid and gas contact efficiency. Modified impeller was then applied in a lab-scale scrubber system for NO gas removal, using ferrous iron ethylenediaminetetraacetate (EDTA), a chelating agent, as an absorbent. With further amendment with an inner impeller, which increases the efficacy of the mesh and impeller blades, 93.6% of the removal efficiency was obtained. Moreover, by increasing retention time via dividing the chamber into two-floor and using two discrete impellers, the efficiency improved to 96.6%. This impeller-based scrubber developed in this study clearly proved to perform exceedingly well in absorbing NO in terms of structural configuration. After modifying the structures and designs of impeller and the scrubber, parametric studies were carried out to increase the NO gas removal efficiency by applying various experimental conditions. With the increase in rotational speed to 3,000 rpm, higher efficiency was obtained, by generating smaller liquid particles. And, when the liquid-gas ratio and absorbent concentration were raised to 20 $L/m^3$ and 0.15M, we achieved up to 97.0% of removal efficiency. Moreover, by applying these ultimate conditions to the two-floor chamber from the previous chapter, the final removal efficiency increased highly up to about 98.6%. The impeller-based scrubber was then applied at Korea South-East power plant in pilot scale for simultaneous SOx/NOx removal. The system includes the scrubber system, activated carbon reactor, and electrochemical cell. In the scrubber system, there is a vigorous mixing between the gas and absorbent (Fe(II)EDTA) to maximize the absorption efficiency for SOx and NOx removal. In the activated carbon reactor, oxidized absorbent was regenerated and then circulated for the continuous operation. And in electrochemical cell, hydrolysis occurred for the pH control. When the entire system was operated, 94.4% of NOx and 99.6% of SOx removal efficiency were obtained, maintaining the efficiency for over 9 hours. Comparing these results with other existing methods, this system was proven to be substantially better than other reported technologies for simultaneous SOx/NOx removal. Impeller-based scrubber system can also be applied in other fields where there includes absorption method of liquid and gas contact. Particularly hydrogen sulfide in biogas, one of serious corrosion-causing compounds, can be treated in the system using Fe(III)EDTA as an oxidant. Using the one-floor scrubber, over 99% removal efficiency of hydrogen sulfide was achieved with 0.05M of the oxidant and 20 $L/m^3$ of liquid-gas ratio. This system can be combined with NOx removal scrubber where Fe(II)EDTA absorbent is oxidized to Fe(III)EDTA in the presence of oxygen, so as for the regeneration process, hydrogen sulfide removal process can be used. By reusing the absorbent after the NOx scrubber as an oxidant of hydrogen sulfide scrubber, 98.1% removal efficiency was obtained, and the solution can be recycled in the NOx scrubber as well. Therefore, a potentially workable integrated system for the removal of both NOx and hydrogen sulfide was proposed with a promising proof of concept results.