STUDY ON THE COMBUSTION AND NOX EMISSION CHARACTERISTICS OF LOW RANK COAL IN A CIRCULATING FLUIDIZED BED WITH POST-COMBUSTION

The combustion and NOx emission characteristics of low rank coal have been investigated in a circulating fluidized bed test plat, which was composed of a circulating fluidized bed (CFB) and post-combustion chamber (PCC). The effects of the air stoichiometric ratio in the circulating fluidized bed furnace and air arrangement in the post-combustion chamber were studied. In the optimized experimental condition, with the air stoichiometric ratio in the CFB ((CFB)) at 0.963, and post-combustion air (PCA) injected into the PCC using ports PCA1 and PCA3, the NOx emission was reduced to 48.7 mg/m(3). The conversion of the fuel-nitrogen in the coal into NOx did not occur under the reducing atmosphere in the circulating fluidized bed furnace. The final quantity of NOx generated from the combustion in the PCC was formed from gaseous HCN and residual nitrogen in fly ash, which flowed with flue gas from the CFB furnace. Enhancing the burnout fraction of coal in the CFB and using the air arrangement in the PCC could effectively reduce the final emission of NOx.