| 90%～95% of NOx is NO in flue gas. We try to find an effective catalyst to turn NO into NO2, and enhance the oxidability of NOx (NO2/NOx) to 50%～60% (at the point we can get a best NOx adsorption efficiency when adsorbed by lye). Then, the NOx after oxidation is adsorbed by desulfurizer (such as calcareousness, NaOH, Na2CO3 and ammonia). If we can realize the processing technique, we can realize desulfurization and denitration simultaneously. The best advantage of the technique is no use of NH3, more simple process, less equipment investment, and no secondary pollution because of NH3 leakiness. The technique is still no actualization in industry by now, and can be the most competitive method.In the technique, catalyst's preparation and performance is the key point. After doing a lot of experiment, we choose Mn/Co-Ba-Al-O catalyst to realize NO oxidation into NO2, and make such research as follows: 1) choose of the catalyst's preparation condition; 2) test of the catalyst's activity; 3) catalyst's characterization 4) test of the catalyst's water-resistent and sulfur-resistent ability; 5) test of adsorption of NOx after oxidation; 6) abecedarian research about the mechanism of the catalytic oxidation reaction.A series of catalyst's preparing factors on activity of the catalyst had studied, including compositionof Co, Ba and Al, content of Mn, calcined temperature of carrier, catalyst's calcined temperature after loading active ingredient and so on. Results show that catalyst whose carrier prepared by parallel-flow precipitation is better than the other two whose carrier are prepared by normal precipitation and reverse precipitation seperately, because the carrier prepared by parallel-flow precipitation has a best crystallinity, largest area surface and without BaCO3. What's more, when Al: Ba: Co=32: 2: 1(molar ratio), MnOx: carrier=20%(mass ratio), catalyst has a best activity.We also tested temperature, velocity, NO inlet concentration, O2 concentration and other factors on catalytic oxidation of NO. Results show that NO conversation into NO2 keeps enhancing with temperature increasing untill 300℃, but falls when the temperature continue increasing for the restrict of thermodynamic equilibrium. When NO inlet concentration increasing, NO conversation into NO2 will reduce. O2 content is in favor of NO conversation into NO2. On the contrary, velocity goes against conversation of NO. On all accounts, when inlet NO volume fraction is 500×10-6, O2 10%, velocity 4000h-1, NO conversation into NO2 can reach 50%～60% at 225℃, 83% at about 300℃, near thermodynamic equilibrium value.Catalyst's activity reduced rapidly when feeding 10%volume fraction of H2O at 300℃accoring to the experiments' result. The possible reason is: H2O can competely adsorb on surface of catalyst as a kind of polar molecule, resulting in reduction of NO active site. When feeding 1×10-3 volume fraction of SO2, NO conversation into NO2 declined sharply. According to the principium making vitriol early, we can conclude that the reaction NO2+SO2→SO3+NO happens when temperature is high. What's more, catalyst's main components Al2O3,BaO(etc.) must turned into vitriol, resulting catalyst's losing activity.Properties of the catalyst were characterized by means of X-ray diffraction (XRD), Brunauer Emmett Teller (BET) and catalytic oxidation mechnism of the catalyst is studied. The adsorption experiment has proved NOx will get a best adsorption efficiency when its oxidability is between 50%～60%.In a word, the research used compound oxide Co-Ba-Al-O with a large surface area as carrier firstly, and made catalyst after loading active compound Mn. The catalyst showed a good activity under low temperature. Under experiment condition, oxidability of outlet NOx can reach 50%～60% at 225℃, exceeding same research result in and abroad, and at 300℃, NO conversation into NO2 is near thermodynamic equilibrium value. So, I believe my research can be a good reference for following study. |
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