96/05277 Method for adjusting coal particle size for carbonization

Abstract

The NO emissions of two anthracitic and three high volatile bituminous coals were experimentally and numerically studied under both air and oxy-fuel combustion conditions in an entrained flow reactor (EFR). Thermal decomposition experiments under N2 and CO2 atmospheres were carried out to determine the distribution of fuel-bound nitrogen between the volatile and char and the results compared with those obtained by means of the network pyrolysis model, FG-DVC (Functional Group-Depolymerisation Vaporisation Cross-linking). This code was also used as a pre-processing stage to predict the evolution of HCN and NH3 during devolatilisation of the coals. A Computational Fluid Dynamic (CFD) model was used to predict NO emissions under different O2/CO2 (21–35% O2) conditions in the EFR.Three different models were used. The first assumed that all of the fuel-bound nitrogen had been converted to HCN. The second assumed that all of the volatile nitrogen would evolve as HCN, and the char–N formed NO by an amount determined by a conversion factor. The third approach was similar to the second but it included NH3 as a precursor of NO as well. The NO emissions predicted with the third approach were in good agreement with the experimental results. A decrease in NO emissions was observed when N2 was replaced by CO2 for the same oxygen concentration for both the experimental and computed results. Higher NO emissions under O2/CO2 conditions were observed when the oxygen concentration was 30 or 35%.