Experimental investigation on combustion and NO formation characteristics of semi-coke and bituminous coal blends

Experimental studies were conducted by thermogravimetric analyzer and drop tube furnace to clarify the cocombustion and NO formation characteristics of semi-coke and bituminous coal. The same experiments were carried out on the blend of anthracite and bituminous coal for comparison. Results indicated that the ignition and burnout temperatures of the blends decreased as the blending ratio of bituminous coal increased, and there existed significant interaction between semi-coke (or anthracite) and bituminous coal. The ignition index C and comprehensive combustion index S presented negative correlations with fuel ratio, and the relationships of C = 6.31-0.35FR and S = 3.87-0.26FR can be used to estimate the co-combustion characteristics of bituminous coal and semi-coke (or anthracite). The addition of bituminous coal gave rise to two competitive effects on semicoke burnout and NO formation. When the bituminous coal accounted for 80%, the promotion on burnout was superior and the inhibition on NO formation was significant. Fuel ratio, rather than nitrogen content played more important role in the NO formation, and relationship of X-No( )= 40.96-4.24N + 1.60FR was established to predict the NO formation during co-combustion of binary coal-based fuels. Besides, semi-coke had better combustion behavior and lower NO conversion ratio compared to anthracite, which mainly resulted from the more porous structure in semi-coke.