烟煤/半焦在循环流化床内混燃时的NO排放特性研究

Research on the NO emission characteristics during the combustion of bituminous coal/semi-coke blends in a circulating fluidized bed

采用电加热循环流化床实验台研究烟煤/半焦混合燃料的NO排放特性,同时为了加深理解,对燃料中N的分布及赋存形式也进行了分析。研究结果表明,神华烟煤中挥发分N和焦炭N的占比分别为53.85%和46.15%,而半焦以焦炭N为主。在燃烧过程中,挥发分N快速析出,并且容易在密相区还原,而焦炭N释放较慢,因而半焦的NO排放明显高于烟煤。在半焦中掺烧烟煤,NO排放量会随其掺烧比的增加而减少,并且燃料之间的交互作用对NO的排放也能起到抑制作用。半焦和烟煤的NO排放量随燃烧温度呈现不同的变化趋势,当半焦中掺烧40%和80%的烟煤时,其排放量随燃烧温度升高而增加。另外,烟煤、半焦及混合燃料的NO排放量随过量空气系数和一次风率的升高也会增加。

The NO emission characteristics of bituminous coal/semi-coke blends were investigated in an electricalheating circulating fluidized bed. Meanwhile, the distribution and occurrence forms of N element in fuels were also analyzed in order to enhance the understanding of NO emission characteristics. The results indicated that the volatile-N and char-N in Shenhua bituminous coal(BC) accounted for 53.85% and 46.15%, respectively, and the majority of N in semi-coke(SC) was char-N. During the combustion, the volatile-N released quickly and was easy to be reduced in the dense-phase zone, whilst the char-N released relatively slowly. Hence, the NO emission concentration of SC was obviously higher than that of BC. After blending SC with BC, the NO emission decreased with the SC blending ratio, and the interactions between component fuels could suppress the NO emission as well.The NO emission of SC and BC showed the opposite variation tendencies with the combustion temperature, and it increased with the temperature for blends with 40% and 80% BC. Besides, the NO emission of BC, SC and their blends all increased with the excessive air coefficient and primary air ratio.