| In recent years, large-scale hazy weather has invaded the most areas of China and air pollution in China became more and more serious. The most stringent NOx emission regulations in history were promulgated to restrict the emission of NOx from stationary sources such as power plant, steelworks and industrial boilers. Thus, developing the cost-effective desulfurization and denitrification technology for industrial boilers becomes the research hotspot. In this paper, ozone oxidation combined with wet absorption process was studied systematically for its promising application prospect. Based on the consideration of the economical performance and absorption efficiency, a simultaneous removal process combined ozone oxidation and wet absorption was investigated in this paper and different sulfite salts were studied as the absorbent of SO2 and NOx.Firstly, ozone oxidation and ammonia-based desulfurization process were combined for the simultaneous removal of SO2 and NOx and ammonia sulfite was used as the absorbent. The effects of ozone concentration, liquid-phase absorbent concentration, pH value, liquid-phase temperature and SO2 concentration on the simultaneous desulfurization and denitrification process were investigated. The results indicated that ozone concentration was a decisive factor for the removal of NOx. When the mole ratio of O3/NO was greater than 1.0, NOx removal efficiency was greater than 80%. In order to ensure the efficiency of denitrification, ammonium sulfite concentration should be larger than 0.012mol/L and pH value above 6.0 was preferred. Temperature of absorbent and SO2 concentration had little impacts on the removal of NOx. Aqueous absorption products of NO2 were investigated, and the results showed the accumulation speed of NO2- decreased due to the reaction between NO2- and NH4+ to produce N2.Secondly, a similar study was conducted to investigate the ozone oxidation combined with calcium-based desulfurization process. Calcium sulfite slurry was the principal absorbent in the liquid. Due to the low solubility of CaSO3 in water, the removal efficiency of NO2 was only 50% when O3/NO was equaled 1.0, which was much lower than that in (NH4)2SO3. Thus, more ozone was needed for the removal of NOx for the ozone oxidation combined with calcium-based desulfurization process. The influences of process parameters in CaSO3 absorption system were similar as the (NH4)2SO3 absorption system.Thirdly, due to the low removal efficiency of NOX, four salts were selected as the absorption additives for the ozone oxidation combined with calcium-based desulfurization process. The results indicated that the addition of ammonium sulfate, magnesium sulfate, ferrous sulfate and manganese sulfate all had the positive effects for the removal of NOx. The addition of additives could lower the consumption of ozone and effectively improved the economy performance of this process.Finally, an industrial demonstration project used the ozone oxidation combined with CaSO3 slurry absorption process was conducted on a 35t/h industrial boiler in a thermal power corporation. Without the addition of additives, the removal efficiency of NOx could reach 80% when the mole ratio of O3/NO was set as 1.4. The emission concentration of NOx of boiler could be decreased to 100mg/m3 when the mole ratio of O3/NO was higher than 1.0. The addition of B additive had a positive effect on the removal of NOx and reduced the mole ratio of O3/NO to 0.8 when the exhaust NOx concentration was matched the emission standard of goverment. |
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