焦炭的非均相反应对循环流化床煤燃烧中 N_2O 生成与分解的影响

Influence of Non homogeneous Reactions on N 2O Formation and Destruction During Combustion of Coal Char in a Circulating Fluidized Bed

在一台小型循环流化床实验台上研究了焦炭的非均相反应对Ｎ２Ｏ生成与分解的影响。实验发现，用同一煤种在不同方式下制取的焦炭燃烧后的Ｎ２Ｏ生成量也有较大的区别；无氧和有氧两种不同的条件下ＮＯ在焦炭表面以两种不同的反应机理转化成Ｎ２Ｏ。氧在焦炭表面的吸附并不是Ｎ２Ｏ生成的必要条件。无氧存在时，ＮＯ也可以在焦炭表面还原生成Ｎ２Ｏ，而有氧条件下ＮＯ在焦炭表面的反应是ＮＯ向Ｎ２Ｏ转化的主要途径，用三种焦炭进行的Ｎ２Ｏ分解试验表明，各种焦炭对Ｎ２Ｏ的催化分解反应都为一级反应，并得出了相应的反应速率常数。焦炭对Ｎ２Ｏ的生成作用大于焦炭对Ｎ２Ｏ的分解作用。

The influences of non homogeneous reactions on N 2O formation and reduction were investigated in a bench scale circulating fluidized bed.The experiments revealed that different kinds of char made from the same kind of coal under different conditions generated different concentrations of N 2O.The mechanism of conversion from NO into N 2O on the surface of char particles in presence of O 2 was different from that in absence of O 2.It was found that absorption of oxygen on the surface of coal char particles was not an indispensable condition for N 2O formation.NO can be reduced into N 2O on the surface of char particles even though there was no oxygen.The mechanism of N 2O formation in presence of O 2 was different from that in absence of O 2.The contributions of these two mechanisms were 70% and 30% respectively.Although N 2O formation through these two mechanisms all increased as temperature increased,the ratio of these two mechanisms did not change significantly.The reaction of NO on surface of char particles in presence of O 2 was the main path of conversion from NO into N 2O. Studies on the types of char suggested that the destruction reactions of N 2O catalyzed by char were all first order reactions,and the kinetic parameters of the reactions were obtained. On the other hand,the effects of different kinds of char on N 2O destruction were quite different,which also counted for the differences in N 2O emissions during combustion of different coals in circulating fluidized beds. Besides that,it was discovered that the contribution of char to the formation of N 2O was greater than that to the destruction of N 2O,which was very likely an important factor responsible for the increase of N 2O along the height of circulating fluidized beds.