Middle East Technical University (METU) 0.3 MWt Atmospheric Bubbling Fluidized Bed Combustor (ABFBC); Volatile Matter/Fixed Carbon (VM/FC) ratios; coal nitrogen; bed hydrodynamics; reactions and rate expressions; volatiles release and combustion; char population balance; char combustion; freeboard hydrodynamics; sulfur retention; NOx formation and reduction; conservation of species and energy; reaction scheme used for NO formation and reduction; characteristics of Beypazari lignite; operating conditions of the experiments