Experimental study on the co-firing and NOx emission characteristics of bituminous coal and its medium temperature pyrolysis char

To address the issues of ignition difficulty, incomplete burnout, and high NOx emissions during coal char combustion in industrial applications, a series of co-firing experiments involving bituminous coal and its medium-temperature pyrolysis char were conducted using a micro fluidized bed analysis system. The experiments explored co-firing behaviors and NOx emission characteristics for five different fuel blending ratios in an environment with 21 % oxygen concentration, across temperatures between 923 K and 1223 K. The study delved into the synergistic effects of coal and char co-firing, as well as the influence of combustion temperature and fuel blend ratio on the co-firing efficiency and NOx emissions. The results show a synergistic effect in the co-firing of bituminous coal and char, influenced by reaction temperature and coal-to-char blend ratio, which evolves as combustion progresses. In the 923–1073 K range, initial coal addition to the blend enhances reactivity. However, as the reaction advances or coal content exceeds 75 %, this synergy shifts to an inhibitory effect. At temperatures above 1023 K, increased proportions of coal in the blend are associated with improved burnout rates, especially when the coal content is at or above 50 %. Moreover, at a combustion temperature of 1123K, there is a marked decrease in nitrogen oxide emissions, with coal blend ratio of 25 % and 50 % showing particular efficacy in reducing these emissions. These results provide valuable insights for the efficient and clean utilization of coal char in industrial combustion processes.