Study On Efficient Removal Of NO_x In Flue Gases By Semi-coke In The Medium Temperature

In recent years,the emission of NO_x in our country has been high,the pollution to environment is becoming more and more serious,and the emission standard of NO_x made by the government is becoming more and more strict,which makes the urgent need to develop NO_x removal technology.Selective catalytic reduction of NO_x with NH3 technology?SCR?has been widely studied,but the equipment investments and operating costs are high,and NH3 is likely to cause secondary pollution caused by leakage of ammonia and form ammonium sulfate with SO2 leading to pipe blockage.Therefore,looking for an economical,efficient and green ammonia substitutes to remove NO_x has become a hotspot in this field.In this dissertation,the semi-coke made by lignite from the Baotou of Inner Mongolia was used to remove NO_x,as a product of incomplete decomposition of lignite,plenty of oxygen-containing functional groups and pore structure were on the surface of semi-coke,which provided favorable conditions for it to remove NO_x efficiently.Besides,abundant reserves,low utilization rate and low price of the lignite could reduce the cost of denitrification.At first,the effects of preparation temperature and preparation time on the removal of NO?NO accounts for more than 90% among NO_x and is difficult to be removed?in simulated flue gases by semi-coke were studied.The results showed that with the increase of preparation temperature and preparation time,the pyrolysis degree of lignite increased,the volatile and the oxygen-containing functional groups of semi-coke decreased,and the ordered structure increased,NO removal rate decreased.The effects of reaction temperature,space velocity and concentration of O2 on the reaction of semi-coke with NO were investigated.NO removal rate decreased first and then increased with the increase of reaction temperature,and the reaction between semi-coke and NO was changed slowly from the chemical adsorption reaction to the reduction reaction.The lower the space velocity was,the longer the contact time was,and the higher the NO removal rate was.Oxygen helped to increase NO removal rate,the higher the concentration of O2 was,the higher the NO removal rate was.Then activated semi-cokes were prepared by single reagent modification and double reagent combination modification with H₂O₂,NaOH and HNO₃.It was found that the specific surface area of modified semi-cokes increased with a different extent,the oxygen-containing functional groups of activated semi-cokes modified by H₂O₂ and HNO₃ increased significantly,and the NO removal rate was higher than that of the activated semi-coke modified by NaOH.The NO removal rate by double reagent combination modification semi-coke was higher than that of single reagent modification semi-coke.However,the NO removal rate was still low and the stability was poor.In order to improve the NO removal rate,Five kinds of different metals,including Cu,Co,Ni,Mn and Fe,were loaded on the semi-coke modified by HNO₃ with impregnation method respectively.the results showed that the NO removal rate increased after the metals were loaded on the activated semi-coke,and Cu,Co and Ni were present in the form of metal,Mn and Fe existed in the form of metal oxides,the NO removal rate by activated semi-coke loaded with Cu,Co and Ni were better than that of the activated semi-coke loaded with Mn and Fe.The effects of Cu content,reaction temperature and concentration of O2 on the NO removal rate by activated semi-coke loaded with Cu were investigated.Cu content was not the more the better,when the content was 2%,the NO removal rate was best.The reaction temperature was a favorable factor for the removal of NO,the higher the reaction temperature,the higher the removal rate of NO,the concentration of O2 was beneficial to the removal of NO,but the concentration was too high,the NO removal rate would decline.Although the NO removal rate was improved greatly after metals loading on the activated semi-coke,the stability of NO removal rate was still poor.In order to further improve the denitrification performance of activated semi-coke,Cu O/SC catalyst was successfully prepared by hydrothermal method.Cu O content was increased with the preparation temperature and time.When the preparation conditions were 120 oC and 2 h,the size of Cu O was small,and the dispersion was well.When the preparation time was 4 h,flower-shaped Cu O was loaded on the activated semi-coke.The effects of Cu O preparation conditions,C-NO reaction temperature,space velocity and concentration of O2 on NO removal rate were studied.The results showed that when the preparation temperature was 120 oC,the preparation time was 2 h,the reaction temperature of was 250 oC,The space velocity was 19200 h-1,concentration of O2 was 4%,the NO removal rate was up to 95.26%,and the stability was improved greatly.