Effects of ethanol
injection on NO
x
removal performance in
an ozone advanced oxidation process were
investigated based on a scale-up reaction system. Experimental results
showed that the introduction of ethanol in simulated flue gas could
enhance NO
x
removal performance greatly
in the O3–ethanol–NO
x
system. With an initial NO concentration of 400 ppm in flue
gas at 150 °C, the injection of 200 ppm O3 could oxidize
approximately half of NO into NO2. When further introducing
∼150 ppm ethanol vapor in flue gas, the outlet NO concentration
would drop sharply to ∼68 ppm while outlet NO2 concentration
would drop down to ∼165 ppm at the same time. This enhancement
effect was ascribed to a synergistic reaction between O3, ethanol, and NO
x
in the gas phase.
The gas reaction products were analyzed by using gas chromatography–mass
spectrometry, and some kinds of nitro-compounds, such as nitroso methane,
nitromethane, nitric acid methyl ester, and nitric acid ethyl ester,
had been found. It is implied that some complex reactions might occur
between ethanol and O3 at the presence of NO
x
, in which a large number of organic radicals and
hydroxyl radicals had been produced. In addition, the effects of key
operating parameters on NO
x
removal performance
were investigated through comparing the changes in the NO
x
concentration between O3–NO
x
and O3–ethanol–NO
x
systems, and the related reaction mechanism
had also been discussed.
The stringent international regulations on marine emission abatement have exerted a huge push on the development of marine desulfurization and denitrification technologies. However, for the traditional vessels driven by large two-stroke diesel engines, simultaneous removal of NOx and SO2 is still a big challenge at present. Here, a one-stage ozone oxidation combined with in-situ wet scrubbing for simultaneous removal of NO and SO2 is proposed. A series of experiments were performed based on a bench-scale reaction system. The results showed that in-situ wet scrubbing could effectively decrease flue gas temperature, and then suppress the thermal decomposition of ozone, which was beneficial for improve oxidant utilization. Meanwhile, the in-situ combination of ozone injection and wet scrubbing was in favor of improving the selectivity oxidation of NO over SO2 by ozone, which was possibly due to the high aqueous solubility of SO2 in water. Aiming to reduce the electric power consumption by an ozone generating system, O3/NO molar ratio was kept as low as possible. A complete removal of SO2 and a high NOx removal efficiency could be achieved through the introduction of other oxidative additives in scrubbing solution. This integrated system designed for marine application was of great significance.
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