Experimental Study Of Catalytical Reduction Of Nitrogen Oxide By Iron

Nitrogen oxide (NO) is a major pollutant emission from coal-fired boilers, which is very harmful to human health and the environment. It is very important to study effective and low cost technologies of NO reduction from the point of view of both academic understanging and industrial application. In this thesis, the author proposed a novel method to reduce NO emission which is based on iron catalysis and conducted detailed experimental tests and mechanism analysis.First, recent development of NO control technologies was comprehensively reviewed based on literature research. Two typical methods, e.g., reburning and selective catalysis reduction (SCR) were particularly introduced. The shortcomings and the hot topics related to reburning and SCR were discussed in detail. The previous research work on NO reduction by iron and its oxides were discussed and the present research methods were then proposed.In this thesis, Iron mesh rolls were selected as iron samples to catalytically reduce NO. Experiments were carried out in a ceramic tube reactor with a simulated flue gas consisting 0.05%-0.1%NO in a nitrogen base. A one-dimensional ceramic tube of inner diameter of 2.5 cm was used as the reactor and was electrically heated in the temperature programmed furnace. The total heated length of the reactor was 30 cm. The flow rate of the flue gas was 1.5 L/min. Several groups of iron meshes with different length and width were used in the tests. The size of the basic mesh unit was 6mm X 6mm and the diameter of the mesh wire was 0.5 mm. The mesh was first rolled into a mesh roll a little thinner than the tube inner diameter and then the mesh roll was horizontally set in the center of the heated tube. The tests were conducted in the temperature range of 300℃to 1200℃. The effect of different gas agents including CO, CO2 and O2 were examined. An online analyzer (ECOM-J2KN, Germany) was used to monitor the gas species. The surface micro-structure and component changes of the rion samples were analyzed by X-ray diffraction (XRD) and scanning electrical microscope (SEM) methods.The following main conclusions can be drawn from the results. (1) In inert atmosphere, the results showed that iron mesh roll was very effective to catalytically reduce NO to N2. The sample with a size of length X width =160mm×80mm had the best effect under the experimental conditions. NO removal efficiency was higher than 95% above 680℃.(2) CO can promote the NO catalytic reduction by iron. When 0.1% CO was fed into the reactor, the NO reduction efficiency by iron approached 95% at 600℃, 180℃temperature drop for the similar NO reduction efficiency compared to that in inert atmosphere. Results showed that the higher the concentration of CO, the higher NO reduction efficiency by iron became.(3) Experimental results demonstrated that O2 had a negative effect on NO reduction by Iron, At 1050℃, NO removal efficiency was about 99% in inert atmosphere, while it dropped to be 90% when 0.5% O2 was fed into the reactor. As oxygen concentration was 1%, NO removal efficiency dropped to 80%, when oxygen concentration was 2%, NO removal efficiency dropped to 60%, when oxygen concentration is 4%, NO removal efficiency dropped to 35%.(4) Results showed that CO2 had a negative effect on NO catalytic reduction, but negative effect will be negalected when the temperature is higher than 700℃.(5) In simualtied flue gas consisting 16.8% CO2, 1%-2% O2 and 0.05% NO, iron mesh roll was also effective to reduce more than 90% NO at certain temperature conditions. The results showed that when the CO concentration was 4%,02 concentration was 1%, the NO removal efficiencywas up to 90% above 650℃.Finally, author tested the oxide Iron by scanning electron microscopy (SEM) techniques and X-ray diffraction (XRD) technique. SEM Test results showed that the porous, fluffy surface structure of the iron mesh roll formed in inert and reducing atmosphere helped iron absorption of NO, so NO can penetrate into the inner layer of iron samples easily, and promoted NO removal by Iron; on the contrary, the dense, smooth surface structure of the iron mesh roll formed in oxidizing and simulated gas atmosphere was harmful to the catalytic reduction of NO by iron. XRD results showed that iron was oxidized to Fe+2Fe2+3O4 and Fe2O3, in an inert, oxidizing and simulated gas atmosphere, FeO in the reducing atmosphere, and FeO, Fe+2Fe2+3O4 and Fe2O3 in CO2 atmosphere, respectively.