| Atmosphere is one of the most basal environment elements for human's survival, the air quality will directly relate to people's healthy status and the development of ecological environment. China is the world's largest coal manufacture and consumption countries, coal combustion resulted in serious air pollution, especially NOx of coal-combustion flue gas. The dissertation amply introduced the existing domestic and international flue gas denitrification techniques, and aiming at the pollution actuality of NOx in our country, investigated and empoldered a newly simple, cheap, practical flue gas denitrification technique, which is applicable to medium-sized and small-sized boilers.After comparing synthetically, urea wet flue gas denitrification was chosed as an investigative base point of this task. Firstly, the feasibility of urea wet flue gas denitrification was analyzed from the perspective of chemical reaction thermodynamics, and compared with hydrogen peroxide, the result showed that both of them could achieve the removal of NOx from flue gas, but the NOx removal rate of urea was better. At the same time, through deducing the relation between reaction temperature and balance branch pressure of NOx, the result showed that rising reaction temperature went against denitrification reaction.The experimental of urea wet flue gas denitrification was investigated in a semi-batch bubbling reactor, educed the effect of reaction time on the removal rate of NOx with urea technique, and calculated the average NOx removal rate in 20min was 33.9%. Aimming at the low removal rate of NOx with using urea only, put forward an original opinion, that is, through adding Co(en)33+ in the urea solution to increase the solubility of NOx and the oxidation degree of NO2, thereby achieve the purpose of increase removal rate of NOx. After comparing with several other additives, the results were as follows:KMnO4> Co(en)33+> H2O2> TiO2. KMnO4 easily led to the color pollution of solution, which was more difficult to dispose. Co(en)33+could generate complexation hydronium with NO, increase the solubility of NOx and the oxidation rate; Co(en)33+ is the catalyst of the reaction, superfluous ethylenediamine could make the complex rebirth, and the absorption solution could be reused. Therefore, Co(en)33+ was chosed as an additive of urea wet flue gas denitrification.Basis of this foundation, the technique of Co(en)33+ complexation and urea deoxidization was investigated. Anaylzed the effects of NOx concentration, Co(en)33+ concentration, urea concentration, oxygen concentration, flue gas flux, pH and reaction temperature on the removal rate of NOx, and regressed the empirical formulas of various factors. Concretely results were as follows:(1).NOx concentration, Co(en)33+ concentration and oxygen concentration in direct proportion to the NOx removal rate; (2).Urea concentration had little impact for the NOx removal rate;(3).Increasing flue gas flux went against the removal of NOx; (4).Alkaline conditions were propitious to raise the rate of denitrification, however, when the pH exceeded to 10.6, the NOx removal rate dropped; (5).Rising temperature was conducive to enhancing the rate of denitrification, especially over 50℃, the NOx removal rate heightened to a larger, but when the temperature rose to 70℃, the NOx removal rate declined rapidly. After comparing synthetically, the feasible experimental conditions were concluded:Co(en)33+ concentration 20mmol/L; urea concentration 0.5～1.0mol/L; pH 10.6; temperature 63℃. At the same time, an continuous experiment of NOx removal from flue gas was investigated by using Co(en)33+ complexation and urea deoxidization, the results show that:at the existing experimental conditions, this technique could keep stably operation in one hour.The flue gas denitrization technique of Co(en)33+ complexation and urea deoxidization has the following advantages:process flow simple, low investment and operating costs, operation and maintenance convenience, without secondary pollution. It's a new flue gas denitrification technique, which is applicable to the medium-sized and small-sized boilers. The abroad application of this technique could decrease the NOx concentration, improve air quality, and have good environmental, economic and social benefits. Therefore, the study has some theoretical significance and applied value, and could make a further extension in industry. |
PDF Full Text Request