| Coal-fired industrial boiler is an important part of energy power equipment in China. Up to now, research on the technology of combined removal of flue gas pollutants in small and medium sized boilers is very limit, which can not meet the needs of current market. In this thesis, a novel simultaneous desulfuration and denitrification technology aiming to treat the medium and small industrial boiler flue gases was developed. This technology was based on a well-reported wet flue gas desulfuration process, which combined a gas phase O3 oxidation process and a subsequent wet MgO absorption process.Firstly, the oxidation processes of NOxand SO2 by O3 were analyzed by using an in-situ FTIR spectra, which revealed that under the oxidation temperature at ca.80? and the inlet molar ratio of O3/NO less than 1, NO was mainly oxidized to form NO2, whereas as the ratio increased to more than 1, the NO was further oxidized to N2O5 (or HNO3). NO3 was a key intermediate product for N2O5 and HNO3 generations, the formation of which was temperature dependence. Moreover, when the reaction temperature was higher than 100?, the increase in reaction temperature could inhibit the formation of HNO3 and N2O5 and the oxidation reaction tended to generate NO2. Besides, the O3 seemed to had no effect on SO2 oxidation, which showed remarkable selectivity to NO oxidation if the coexistence of NO and SO2.Secondly, pure water, nitric acid, magnesium, sodium and calcium based sorbents had been employed for absorptions under different O3 injections. The effects of process parameters on respective absorption efficiencies were investigated. It was found that the NO2 could be partly absorbed in neutral and alkaline aqueous solutions where the N2O5 could be effectively absorbed (generally achieving 100% efficiency) under all investigated conditions.Thirdly, the effects of process parameters and corresponding absorption mechanism of NO2 and SO2 in magnesium based slurry were studied. It was found that the pH value, initial concentration of SO2 and concentration of MgO can all affect the absorption efficiency of combined desulfurization and denitrification process. When the absorption solution pH and MgO concentration were appropriate, the absorption efficiency of NO2 can reach up to 75%. The absorption efficiency of SO2 could be achieved at a high level (i.e. approaching 100%) when the pH of MgO slurry was above 4. Studies on absorption mechanism had showed that the Mg2+ could react with SO32- forming (MgSO3)0 neutral ion pairs, which could react with NO2 to improve the absorption efficiency for the slurry.In the end, the thesis studied the effects of different additives on the absorption efficiency in wet combined desulfurization and denitrification process. After the addition of triethanolamine (TEA) in magnesium based slurry, the absorption efficiency of NO2 could be improved to almost 100% under alkaline condition. In acidic condition, the TEA did not reveal such enhanced effect. This was due to that the N atoms with unpaired electrons could reflect a reduction feature in alkaline condition. Moreover, the NO2 absorption efficiency could be also effectively improved by adding ascorbic acid (Vc) into the magnesium based slurry, the mechanism of which was ascribed to the addition of ascorbic acid could inhibit the oxidation of SO32- ions into SO42- ions. |
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