To investigate the issues associated with burning lean coal in circulating fluidized bed boilers and to address the limitations of traditional experiments—which lack research on combustion characteristics in the dense phase and the initial formation of nitrogen oxides—this study established a small-scale fluidized bed test rig to simulate combustion conditions in the dense phase of a fluidized bed boiler. The study analyzed the formation and concentration of nitrogen oxides in the dense phase, as well as the composition of fly ash and bottom ash. The results indicate that under simulated dense-phase combustion conditions with only primary air supply and an air-fuel ratio of 0.5, the initial NOx formation decreases with increasing temperature and decreasing apparent fluidization velocity. Conversely, the initial NOx formation increases as the air-fuel ratio increases. Furthermore, higher temperatures, lower apparent gas velocities, and higher air-fuel ratios all contribute to improved carbon conversion. Regarding the influence of fuel, fuel with a smaller average particle size exhibits better combustion characteristics and lower initial NOx formation compared to fuel with a larger average particle size; similarly, fuel with a narrower particle size distribution performs better than fuel with a wider distribution. When generating electricity by burning lean coal in power plant boilers, increasing the primary air flow rate, reducing the primary air velocity, and decreasing the average particle size of the fuel can improve combustion efficiency and reduce initial NOx formation.
Ni et al. (2026) studied this question.