SNCR技术水泥脱硝氨水脱硝反应动力学机理分析

Mechanism analysis on ammonia denitration reaction kinetics of cement denitration of SNCR

SNCR烟气脱硝技术中最主要的化学反应是氮氧化物与氨气的反应。文中揭示了氨气脱硝的反应机理,从而有助于提高脱硝效率,提出并建立了NO,NO_2,O_2和NH_3反应动力学模型。通过模型计算,分析了NO-NH_3、NO_2-NH_3和O_2-NH_3反应吉布斯自由能、反应速率常数,以及反应温度对反应速率的影响。由结果可知:温度在1 000—1 400 K的范围内,NO-NH_3,NO_2-NH_3和O_2-NH_3反应能自发进行,反应限度很深;在相同浓度、反应温度的条件下,NO_2-NH_3,O_2-NH_3和NO-NH_3的反应速率常数逐渐变小,反应温度的升高对于NO-NH_3,NO_2-NH_3反应的影响不明显,但对于提高O_2-NH_3反应的效果非常明显,即在相同的条件下,O_2比NO,NO_2更容易与NH_3反应。结论表明,在水泥回转窑的实际生产过程中,应严格控制过量空气系数。

The reaction of nitrogen oxides and ammonia was the top-drawer reaction of SNCR flue gas denitrification technology. The mechanism of ammonia denitrification was revealed so as to improve the denitrification efficiency,the reaction kinetic models of NO,NO_2,O_2 and NH_3were established and the effects of Gibbs energy,reaction rate constant of NO-NH_3,NO_2-NH_3 and O_2-NH_3 on reaction rate were analyzed. The results show that NO-NH_3,NO_2-NH_3 and O_2-NH_3 are spontaneous reaction,the NO-NH_3 reacts with NO_2-NH_3 and O_2-NH_3 spontaneously at a large extent equilibration when the temperature is 1 000-1 400 K. At the conditions of same temperature and concentration,the reaction rate constants of NO-NH_3,NO_2-NH_3 and O_2-NH_3 become smaller gradually. It has no obvious influence to improve the reaction rate constant of NO-NH_3,NO_2-NH_3,but for improving reaction rate constant of O_2-NH_3 is very evident,which shows that O_2 more easily reacts with NH_3 compared with NO and NO_2.Therefore the excess air ratio should be strictly controlled in the actual production process of cement rotary kiln.