Experimental investigation on the ignition and combustion characteristics of pyrolyzed char and bituminous coal blends

Abstract This work studies the ignition behavior and combustion characteristics of pulverized pyrolyzed bituminous (PB) char blended with pulverized bituminous coal at different mass fractions. Experimental studies were conducted with OH planar laser-induced fluorescence (OH-PLIF) diagnosis technology in a flat-flame optical entrained flow reactor for pulverized coal/char. An interaction occurs between pyrolyzed char and bituminous coal, which is indicated by the relationship observed between the pyrolyzed char mass fraction mean values (MFMVs) and the combustion properties of the blended fuels. The addition of bituminous coal enhances the competitive effects of the two fuels on ignition and burnout. The synergistic effect observed upon ignition of the blends is mainly attributed to the high volatile contents and the potential catalysis effects from the alkali and alkaline earth metal species in the blends. The important factor leading to this synergistic effect is that the alkali and alkaline earth metal species in the ash can reduce the ignition temperature and accelerate the release of volatiles, thereby shortening the ignition delay. The high flame temperature and the potential catalysis effects from the alkali metal and transition metal species promote blended fuel burnout. Considering both the ignition delay and the residual char burnout, the optimal blending ratio of pyrolyzed char is approximately 20% because the fixed carbon burnout of the blends is considerably promoted and the ignition delay is significantly shortened. In comparison with PB char, the ignition delay decreased by 28.95% and the burnout ratio increased by 39% at the 20% PB char blending ratio.