Numerically Study on Combustion and NO_x Emission Characteristics in Tangentially Fired Boiler Co-Firing Semi-Coke

Semi-coke is a specific solid fuel, which is mainly produced by upgrading low-rank coal. The poor reactivity of semi-coke makes a difficulty to its practical utilization in utility boilers. Previous research was mainly focused on the combustion behavior of semi-coke, while the industrial application has to be understood. In this paper, the effect of co-firing semi-coke and bituminous coal on the operation performance of pulverized boiler was numerically studied. The work was conducted on a 300 MW tangentially fired boiler, and the temperature distribution, the char burnout and NO_x production were mainly examined. The results indicate that the incomplete combustion heat loss drops with the increase in semi-coke blending ratio. The NO_x concentration increases from 186 mg/Nm³ for only firing the bituminous coal to 200, 214, and 255 mg/Nm³, when the blending ratio was 17%, 33% and 50%, respectively. With enhancing excess air coefficient for the co-firing condition, the combustion efficiency got improved, while NO_x production increased very slightly. In general, the boiler is well adapted to co-firing semi-coke, and the semi-coke blending ratio of 1/3 with an excess air coefficient of 1.235 is recommended.