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

The NO emission characteristics of bituminous coal/semi-coke blends were investigated in an electrical-heating 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.