Effect of additives on the combustion characteristics of coal pellet clusters and the release characteristics of sodium alkali metals

Hyperspectral imaging technology was employed in this study to investigate the release characteristics of alkali metals Na during the combustion of NMH lignite coal. Flame images were captured under varying particle sizes and flow rates, and optical filters were utilized to detect the two-dimensional distribution of Na under various operating conditions. Additionally, the impact of solid additions on the adsorption performance of Na was evaluated. The results show that NMH particles exhibit a combination homogeneous-heterogeneous igniting mode under different setting. It has been found that ignition delay time and combustion duration are reduced by smaller particle sizes and higher oxygen volumetric flow rates. The peak concentration of Na releases is found in the middle, with lesser quantities surrounding the perimeter. As particle size decreases and oxygen flow rate increases, the central sodium concentration region is expanded, and a more extensive distribution area is established. It is shown that the release of alkali metal sodium is inhibited by both single additives (SiO₂, Al₂O₃) and mineral additives (kaolin, diatomite), which also affect the ignition delay time and the duration of each combustion stage.