Formation of volatile nitrogen compounds during coal pyrolysis and devolatilization

摘要

The major advantages of fluidized bed combustion (FBC) are fuel flexibility and low emissions of SO(sub 2) and NO(sub x). The low emission of NO(sub x) is partly due to the low combustion temperatures of about 1050 to 1150 K, and partly to the staged combustion principle of FBC. However, the relatively low combustion temperature increases the emission of N(sub 2)O compared to other combustion systems. The emissions of NO(sub x) and N(sub 2)O from FBC are very dependent on a number of operating conditions, and many homogeneous and heterogeneous reactions are important for their formation and destruction. During devolatilization fuel nitrogen is split in char nitrogen and volatile nitrogen compounds, which are mainly tar, NH(sub 3) and HCN. During combustion the char nitrogen is oxidized to NO and N(sub 2)O and simultaneously partly reduced to N(sub 2), but also small amounts of NH(sub 3) and HCN may be formed. The volatile nitrogen may be oxidized to NO, N(sub 2)O or N(sub 2) or may take part in the reduction of NO and N(sub 2)O together with CO and H(sub 2) homogeneously or heterogeneously with char, limestone, ash and sand as catalysts. The information of volatile nitrogen compounds during coal pyrolysis and devolatilization is considered, based on a survey of relevant literature. (AB) 52 refs.