微细化煤粉再燃还原NO的反应动力学机制

Dynamics Mechanism Governing a NO Reduction Reaction During the Reburning of Superfine Pulverized Coal

以3种细度的混煤(烟煤与褐煤)、一种细度的大同烟煤和邢台贫煤微细煤粉作为再燃燃料,用N2、O2、CO2、NO配制模拟烟气,在1 300℃和1 100℃立式管式携带炉中进行了再燃还原NO的实验研究,对其化学反应动力学机制进行了分析。实验结果表明,微细化煤粉再燃还原NO的化学反应速率受扩散———反应动力学联合控制。因此,提高再燃区温度水平、使用反应活性高的煤粉作为再燃燃料或者提高再燃煤粉的细度,均能够明显提高再燃还原NO的化学反应速率,从而可以适当缩短煤粉在再燃区的停留时间。但是,如果再燃区停留时间低于0.6 s,NO的还原效率会大幅度下降,同时也会导致煤粉燃尽率的降低。采用微细化煤粉作再燃燃料,再燃区的适宜停留时间约为0.8 s。

With blended coals(bitumite and lignite) in three kinds of fineness,Datong-origin bitumite in one kind of fineness and Xingtai origin lean coal in the form of superfine pulverized coal all serving as reburning fuel,and having prepared a simulation flue-gas by using N_2,O_2,CO_2 and NO,an experimental study was conducted of NO reduction by reburning in a(1 300) ℃ and 1 100 ℃ EFR(entrained flow reactor) along with an analysis of its chemical reaction dynamics mechanism.The experimental results show that the chemical reaction rate of superfine pulverized coal reburning involving NO reduction is jointly controlled by diffusion——reaction dynamics.Hence,raising the temperature in the reburning zone,using pulverized coal with a high reaction activity as reburning fuel or increasing the fineness of reburned pulverized coal,all these measures can significantly enhance the chemical reaction rate of NO reduction through reburning,thereby properly shortening the residence time of pulverized coal in the reburning zone.However,if the residence time of the pulverized coal in the reburning zone is shorter than 0.6 s,the efficiency of NO reduction will drop drastically.Meanwhile,the pulverized coal burn-out rate will also be reduced.It has been found that with superfine pulverized coal serving as a reburning fuel,the suitable residence time in the reburning zone should be about 0.8 s.