Industrial-scale Investigations on Combustion Characteristics and NO<i><sub>x</sub></i> Emissions of a 300-MW<sub>e</sub> Down-fired Boiler: Bituminous Coal Combustion and Coal Varieties Comparison
Xin Zhang, Zhichao Chen, Liankai Li, Lingyan Zeng, Zhengqi Li
Abstract
Number of down-fired boilers burning bituminous coal or anthracite blended with bituminous coal has exceeded 10% of the total down-fired boilers in China. However, lacking of the industrial-scale research on the performance of down-fired boiler burning bituminous coal or blended coal, which limits the actual operation adjustment. Industrial-scale experiments on a 300-MWe down-fired boiler fueled with bituminous coal and blended coal were performed, which boiler was originally designed to burn low-volatile coal. Without the over-fire air, air-staging combustion can still be realized when the down-fired boiler burning bituminous coal. The combustion performance in the down-fired boiler under different coal varieties was compared. Compared with the anthracite case, flue gas temperature is higher, coal flame fullness is greater, O2 consumption occurs faster and NOx concentration is lower in the primary combustion zone when burning bituminous coal. Strong reducing atmosphere is formed in the primary combustion zone. The NOx emissions are low at a level of 410 mg/m3 at 6% O2 at furnace exit and boiler thermal efficiency reaches 92.590% when burning bituminous coal. The NOx emissions cannot be further reduced by burning blended coal. In addition, the boiler thermal efficiency reduced by 1.108%. Without the over-fire air, compared with burning anthracite or lean coal, the NOx emissions and carbon in fly ash significant reduction by 70% and 90%, respectively, and the boiler thermal efficiency increased when burning bituminous coal.