Study On Removal Of No_x In The Coke Oven Flue Gas Using Microwave Coupled With Coal-based Carbon

With the development of industry，the environment problem is getting more serious,especially the emission of NOx, which has attracted widespread attention in recent years. NOxis one of the main causes of air pollution because it can cause fog haze, photochemical smogand acid rain. The control emission of NOxwas focused on coal-fired power plants andautomobile exhaust before. However, we did not pay enough attention on the emission of NOxfrom coking industry. The new “standard of pollutant discharge on coking chemical industry”(GB16717-2012), published in June27,2012, made a more strict requirement on the NOxemission of coking industry. In order to control the emission of nitrogen oxides and thus adaptto the new environmental protection policy, coking industry should not only improve the cokeoven design and heating technology, but also introduce the exhaust gas denitration technology.At present, SCR, SNCR and wet denitration technology are widely used, but thesetechnologies have some general problems such as high cost and secondary pollution fromby-products. So it is urgent to find a green denitration technology with low cost and highefficiency for coking industry. Considering the characteristics of the coking industry itself,microwave irradiation technology was employed in the present research, and the coal-basedcarbon was used as adsorbent and reducing agent, so as to achieve a high efficiency of NOxremoval in the flue gas of coke oven. The main conclusions are as follows:(1)By comparing the denitration performance of different sources of coal-based carbonunder different microwave power, we found that the coal-based carbon prepared by lowquality coal had better denitration performance, which could reached to95.88%~98.10%inthe microwave power of300w, slightly lower than the product of coal based activated carbon(denitration rate100%). While the denitration of coal-based carbon prepared by coking coalblending was only55.90%~60.56%. FTIR showed that low quality coal contained rich polarfunctional groups, which could promote the adsorption of NOxand transformation ofmicrowave energy. Thus low quality coal is a kind of microwave denitration carbon materialwith low cost and high efficiency.(2)The infrared thermal imager study showed that the temperature distribution ofcoal-based carbon was not uniform in microwave field. The high temperature zone concentrated in the center area of the coal-based carbon. When the microwave power andcoal-based carbon quality were fixed in microwave field, the coal-based carbon had anextreme temperature, denoted as Tmax, which increased with the increase of the power. Whenthe coal-based quality and microwave power were20g and100~300w respectively, Tmaxand microwave power (P) followed Tm ax232.18ln(P)879.7.(3)The denitration performance of coal-based carbon increased with the increase ofmicrowave power, coal-based carbon quality and residence time, while decreased with theincrease of flow and space velocity.92.35%of NO was eliminated in the condition ofmicrowave power250w, Tmax>400℃, coal-based carbon quality20g, flow rate of exhaustgas1000ml/min and NO concentration268mg/m3in flue gas. When the concentration of NOchange to268~804mg/m3, denitration rate reached84.25%~92.35%. The addition of O2can promote the denitration, when increasing the oxygen content from0%to4%, thedenitration rate increased from90.00%to94.34%. While the addition of CO2haddisadvantage of denitration, when increasing the CO2concentration from0%to5%, thedenitration rate decreased from89.72%to81.35%. The denitration rate increased from91.35%to93.98%after2%water vapor was added in flue gas. But the denitration rate beganto reduce when the content of water vapor increased to4%.(4)The kinetics study of microwave coal-based carbon denitration showed that thereaction rate followed50.66ex23.62103NOp(8.314T)CNOin the rapid reaction zone.Reaction activation energy of the microwave-coal carbon denitration dropped from64kJ mol–1of conventional heating to23.62kJ mol–1.(5)Copper, cobalt and nickel metal matrix coal-based carbon catalysts were prepared byisometric impregnation method, respectively. The denitration rates of these three catalystswere96.91%,93.6%and94.87%, respectively, in the microwave power of250w, whichproved copper base coal-based carbon showed the best catalytic performance. Copper basecatalyst was characterized by XRD, SEM and EDS, showed that the main catalytic effectcame from CuO, which attached to the surface and pores in the carbon with irregular thinsheet. (6)Microwave-copper coal-based carbon denitration technology was verified by theorthogonal experiment in the treatment of simulated flue gas. The results showed that thefactors affecting the denitration rate were: power (temperature)>flue rate> quality ofcoal-based carbon> dosage of coal-based carbon catalyst. Under the optimum reactionconditions (P=300w, L=300ml/min, m=30g, ωCu=0.5%), the denitration rate ofsimulation coke oven flue gas was96.62%by microwave-copper coal-based carbon. The NOxconcentration decreased from410mg/m3to13.86mg/m3which was far lower than thenational emission standards, achieving the treatment of coke oven flue gas with low cost, highefficiency and green.