| In recent years,with the rapid development of ultra-low air polluntants control technologies in power plant boilers,coal-fired industrial boilers take place of power plant boilers and to be the largest stationary source in NOx emissions.In this thesis,sodium sulfite was used as absorbent to investigate the influence of operating parameters on denitrification performance for the aqueous absorption process which is most suitable for the small and medium-sized industrial boilers.Besides,a small industrial experiment was conducted in a packed tower reactor for the potential industrial applications.At last,a novel treatment process for denitration wastewater that mainly contained NO2-was tested to realize the complete detoxification of NOx.Firstly,NO2,the main product of the forced oxidation of NOx,was used as the simulated air pollutant in the experiments.Experimental results indicated that the denitration efficiency increased effectively with the concentration of Na2SO3 enlarged,whereas the absorption rate also increased with the increasing of NO2 concentration under experimental condition.When the pH value was above 6.5,the denitration efficiency maintained at 90%.If the pH value decreased gradually,the denitration efficiency showed an obvious decline trend,while the concentration of SO2 increased due to the side reactions that occured simultaneously.Besides,when the oxygen content in flue gas was above 3%or the NO2-concentration in liquid phase was above 2.86 mol/L,the denitration efficiency declined apparently.The temperature of absorption liquid and the concentration of SO2 in flue gas had little impacts on the denitration efficiency.In addition,the increasing stirring speed was favorable to NO2 absorption.Aqueous absorption products of the wet denitrification process were also investigated,and the results showed that NO2-was the main liquid product of NO2 absorption.However,as the acidity of the absorbent or the molar ratio of HSO3-to NO2-increased,the reaction between NO2-and HSO3-was accelerated and there were sulfur-nitrogen compounds formed.When pH value dropped to 4.5 or the molar ratio of HSO3-/NO2-increased to 4,NO2-would be converted to sulfur-nitrogen compounds entirely.A further study on wet denitrification in packed tower was investigated for the potential industrial application.The results indicated that the packed tower with polyhedron empty ball packings achieved a great denitrification performance.The optimum concentration of absorbent was 0.16 mol/L.Within the range of experiment,NO2 removal efficiency was enhanced by the increasing of NO2 concentration,whereas the denitrification efficiency maintained stable when the NO2 concentration was above 120 ppm.Increasing the packing height and the liquid-gas ratio could promote the NO2 removal performance effectively.However,increasing the gas velocity was unfavorable to wet denitrification process.The absorption efficiency of SO2 was higher than 98%in the packed tower,and the variation of SO2 concentration slightly affected the removal of NO2.The denitration efficiency of the small industrial experiment with 200 N/m3 packed tower was 77.88%.For the treatment of denitrification wastewater with high concentration NO2-,experiments on NO2-removal were conducted by using sulfamic acid as reducing agent,which could reduce aqueous NO2-into harmless N2.The effects of operational parameters on NO2-removal were studied.Results showed that when the pH value of sulfamic acid solution was around 2.0-3.0,the NO2-removal efficiency could reach 100%and the concentrations of by-products,such as NO3-and NOx,were the lowest among the tested pH value range.The NO2" concentration,the temerature of solution and the presence of other interfering ions had little impacts on the removal of NO2-·Under the method of pipeline mixing,the removal efficiency of NO2-increased with the increase of mixing time.When the mixing time was above 5 s,the treated wastewater could meet the discharge standards for industrial wastewater. |
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