Experiment study on NOx emission characteristics of the ultra-low volatile fuel in a 2 MW novel pulverized fuel self-sustained preheating combustor

The pyrolysis semi-coke, with ultra-low volatile content, is difficult to burn effectively with conventional combustion technology. In this research, a 2 MW novel self-sustained preheating combustion test rig was constructed. Efforts were made to investigate the effects of secondary air ratio, the air staging degree of preheated fuel burner, and the position of tertiary air on the combustion characteristics and NOx emissions of semi-coke. The results showed that NOx emission was reduced to 67 mg/Nm(3) (@6% O-2) with a combustion efficiency of 99.2%. The internal fluidized bed combustor (IFBC) could provide high-temperature preheated fuel for the combustion chamber steadily. Also, 69.3% of the fuel-bound nitrogen was released in the IFBC. The temperature distribution in the combustion chamber became uniform under the multi-layer arrangement of tertiary air. As the secondary air ratio decreased from 0.50 to 0.40, NOx emissions decreased due to the enhancement of reducing atmosphere in the reducing zone. Besides, the deeper air staging of the preheated fuel burner contributed to forming a region of low oxygen and strong reducibility at the early staged combustion, which could inhibit the generation of NOx. The strong mixing and long dwell time in the reducing zone were essential for the reduction of NOx emissions. The multi-layer and delayed arrangement of tertiary air could reduce NOx emissions significantly. (C) 2020 Elsevier Ltd. All rights reserved.