| Summary: | 碩士 === 國立成功大學 === 環境工程學系 === 87 === We carried out the performance and reaction kinetics studies of individual NOx absorption and the performance study of simultaneous SO2/NOx absorption in a bench-scale spray tower. The component analysis in liquid phase was performed by Ion Chromatography. Because we carried this experiment by using acidic chlorite solution, most of NO molecules were only converted to NO2 molecules in the gas phase and can''t be removed into the solution. Hence, we defined that the percents of the change of NO concentration are NO conversion and the percents of the change of NOx concentration are NOx removal efficiency and the percents of the change of SO2 concentration are SO2 removal efficiency.
In the range of operating conditions for the individual NOx absorption system, the NO conversion is between 2% and 100%, and the NOx removal efficiency is between 2% and 74%. We found that the NO conversion and NOx removal efficiency are increased with the increasing of the NO and NOx concentration, retention time, NaClO2 concentration, and reaction temperature, but are increased with the decreasing of the pH value of solution. The result of effects of parameters on the NOx absorption rate is as same as on the NO conversion and NOx removal efficiency except the retention time. The effects of retention time is insignificant. Remain NOx molecules after absorption are only NO2 molecules when the concentration of solution is raised to 0.04M.
In the simultaneous SO2/NOx absorption system, either NO conversion or NOx removal efficiency with the addition of SO2 are better than without SO2. In the range of operating conditions for the simultaneous SO2/NOx absorption systems, the NO conversion, the NOx removal efficiency, and the SO2 removal efficiency are between 22% and 100%, between 11 and 70%, and between 62 and 98% respectively. Remaining NOx molecules after absorption are only NO2 molecules when the solution concentration is raised to 0.005M.
For the analysis of components in liquid phase and mass balance, the dominant nitrogen species in the liquid phase is nitrate either individual NOx absorption system or simultaneous SO2/NOx absorption system and the dominant sulfate species in the liquid phase are sulfate in the simultaneous SO2/NOx absorption system. The mass balance between gas phase and liquid phase for NOX & SO2 species is quite conservative. In the simultaneous SO2/NOx absorption system, the pH value of solution would decrease to about 2.5, and we can provide the existing of chlorine dioxide by either watching the color of solution or using UV analysis.
For the reaction kinetics study of NOx absorption by NaClO2 solutions, the reaction order for the NO and NaClO2 concentration are 1.8 and 2.1 respectively. The average reaction rate constant is 6.16’107 ((L/mol)2.9/sec). The activation energy for NOx absorption by NaClO2 solutions in this study is 53.86 KJ/mol, the frequency factor is 6.93’1016 ((L/mol)2.9/sec).
According to the experimental data, we get five regression equations shown as below:
(A) The regression equations for the NO conversion and NOx removal efficiency in the individual NO removal system:
NO Conversion=3321.09×([NO])-0.1897×(RT)1.2427×([NaClO2])1.0544×(Temp.)0.3123×(pH)-2.2240
NOx Removal Efficiency=275.90×([NOx])0.3716×(RT)1.2032×([NaClO2])1.0404×(Temp.)0.2424×(pH)-1.5977
(B) The regression equations for the NO conversion, NOx removal efficiency, and SO2 removal efficiency in the simultaneous SO2/NOx removal system:
NO Conversion=851763.45×([NO])-0.5101×([SO2])-0.1763×([NaClO2])0.9787×(pH)0.2265
NOx Removal Efficiency=1913418.64×([NO])-0.6087×([SO2])-0.1126×([NaClO2])1.1881×(pH)0.2657
SO2 Removal Efficiency=1692.37×([NO])0.0193×([SO2])-0.2327×([NaClO2])0.2741×(pH)0.0598
In the individual NO removal system, the effect of NaClO2 concentration on the NO conversion and NOx removal efficiency are the most significant. In the simultaneous SO2/NO removal system, the most important parameter affecting NO conversion, NOx removal efficiency,and SO2 removal efficiency is also NaClO2 concentration.
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