Study On Removal Of No_x From Flue Gas By Modified Semi-coke Catalyst

The emission of nitric oxides from flue gas get more and more,the pollution to the environmen is getting more serious, proper measures could be taken to reduce the harm to the people and environment.Selective catalytic reduction of NOx with NH3 (SCR) technique has been put into commercial application in the NOx disposal, but it is restrained because of the well-known reasons such as storage and leakage of NH3, costly equipment, strict operation conditions and formation of sulfate leading to pipe jam. Therefore, in order to find effective method of removal NOx from flue gas, activated semi-coke has been successfully developed in substitution of activated carbon for removal NOx in the flue gas on the basis of the previous research. Semi-coke is derived from coal pyrolysis at low temperature(600-700℃). Due to the incomplete decomposition process, plenty of hydrogen and oxygen containing functional groups are formed on the surface of semi-coke, as well as pore and surface structure, which provides favorable conditions for it to remove NOx-In this paper, a series of activated semi-coke based catalysts were prepared from raw semi-coke by means of high pressure hydrothermal, HNO3 oxidation, NaOH modification, ozonation, metal oxides loading as well as their combined modification. The results of surface functional groups of alkaline and acid test indicated that:the surface of raw semi-coke was alkaline;The acidic functional groups on the surface of semicoke were increased after semicoke being actived with HNO3 or ozonation, while the alkaline functional groups greatly decreased; the surface of semicoke is acidic. Calcination could rearrange the functional groups that on the surface of semicoke, and make acidic functional groups decompose into alkaline functional groups.The content of alkaline functional groups increased while acidic functional groups decreased. The highest content of surface alkaline functional groups of modified semi-coke is by NaOH treatment and ozonation. The influence of process conditions on NO removal for raw semi-coke and the activated semi-cokes were investigated in fixed bed reactor insimulated raw gas. The results indicated that single or two-step modification could not improve the denitration efficiency remarkably. Among the multi-step combination, denitration activity of FNaO700 was best and the breakthrough time reached 920 min.Then metal oxides loading (Fe2O3, CuO, V2O5) were studied. The research results show that all the metal oxides species had some good effects. Among them, FNaFe1O700 was best among the others with breakthrough time about 1720min.The fixed-bed reactor was applied to evaluate the following parameter which affected the activity of the catalyst:reaction temperature, space velocity, and the content of H2O and O2 etc. The results of experiments indicated that:the reaction temperature had great influence to the denitration activity of semi-coke. The optimum temperature was 80℃, and the optimum space velocity was 800h-1.The existence of O2 in flue gases could enhance the denitration activity of semi-coke, the optimum content of O2 was 5%. H2O in flue gases had poisoning effect on the semi-coke catalyst. Thus the existence of H2O should be avoid in the denitrifi cation operation. The paper employed thermal desorption, water-washing regeneration and hydrous ammonia treatment regeneration to regenerate the deactivated catalyst. The t regeneration temperature and time was also evaluated. The results of experiments indicated that:the regenerated catalysts had lower removal efficiency of NO. Water-washing regeneration was better than the other two. We could see from the experimental results that the optimum regeneration conditions were:regeneration temperature:700℃, regeneration time:1-1.5h.By use of surface area (BET) and scanning electron microscope (SEM) analysis technique, catalyst was evaluated and selected successfully.