Study On The Release Of NO_x Pollutants During The Preparation Of A Copper-based Oxygen Carrier

Oxygen carrier is a key factor restricting the entire chemical looping combustion.In the preparation of oxygen carriers,active metal salts are usually formulated into a solution and supported on a carrier by impregnation,and oxygen carriers are obtained by drying and calcining.In the preparation of oxygen carriers,metal nitrates such as iron nitrate,copper nitrate,nickel nitrate,cobalt nitrate,and zinc nitrate are commonly used as oxygen carrier precursors.Metal nitrates are unstable at high temperatures and decompose nitrogen oxides during drying and calcination.therefore,it is urgent to develop an environmental-friendly method for preparing oxygen carriers.In this paper,it is calculated by studying the thermodynamic equilibrium that NO is the most important component of NOx,NO accounts for more than 99%of NOx emissions,and it is basically free of NH₃.The nitrogen elements of Cu(NO₃)₂ and CO(NH₂)₂ in the oxygen carrier precursor will be converted into NO.When the amount of urea in the fuel is increased,the NO concentration increases rapidly and then decreases;and,when the share of urea in the fuel is about 0.71,it reaches a maximum value.In this paper,Cu-based oxygen carrier precursors were prepared by the sol-gel method.Thermogravimetric,Fourier Transform Infrared spectroscopy,Mass Spectrometry(TG-FTIR-MS)and Differential Thermal Analyzer(DTA)were used to study the evolution and distribution of gaseous products during the calcination of Cu-based oxygen carrier precursors.The effects of reaction temperature,reaction atmosphere,heating rate and different molar ratio of urea to copper nitrate on the pyrolysis characteristics of oxygen carrier precursors and nitrogen oxide emission characteristics were investigated.The main exhaust gas products are H₂O,CO₂,NH₃,N₂,NO,N₂O and NO₂.The release of NH₃and CO₂ increased significantly with the increase of urea content in the oxygen carrier precursor(0.61,0.91 and 1.22 times of theoretical urea content,respectively).When the urea content in the sample is 0.91 times the theoretical urea content,the NOx releases reach the maximum.When the urea content in the sample is 1.22 times the theoretical urea content,the amount and rate of N₂O and NO₂ release are significantly reduced.(The absorbance peak area of N₂O and NO₂ is reduced by 75%and 84%compared with he urea content in the sample is 1.22 times).Compared with the reaction under air and nitrogen atmosphere,the emission concentration of nitrogen oxides(NO₂,NO and N₂O)and NH₃ were reduced by using argon atmosphere.When the heating rate is 10?/min,the NOx emission rate and the amount of NOx emission are reduced(The corresponding peak area and highest peak-to-peak value were reduced by 54%,33%,65%and 63%,66%,82%),and the release rate and the amount of NH₃ is increased(the corresponding peak area and highest peak-to-peak value are increased by 38%and 20%,respectively),increasing the amount of urea added to the oxygen carrier precursor and under the air atmosphere will lead to the release of NH₃about 3 min earlier.The experimental results show that when the urea/copper nitrate molar ratio is 1.22,the Ar atmosphere and the higher reaction heating rate(10?/min)can be achieved a lower NOx emission concentration during the calcination of the oxygen carrier precursor.The higher reaction gas flow rate(120 ml/min)is the lowest concentration of NOx emissions.The DTA curve shows that the calcination process of the oxygen carrier precursor has obvious exotherm,which is beneficial to maintaining the heat required by the muffle furnace and reducing energy loss.In addition,based on the results of XPS,SEM and XRD,the composition and structure of oxygen carriers prepared under different conditions was analyzed.