Towards an efficient metal energy carrier for zero–emission heating and power: Iron powder combustion

In this study, the metal cyclonic combustor (MC²) was utilized to investigate the formation of nanoparticles (nPMs) and NO_x during the combustion of iron powder under varying input conditions of equivalence ratio and oxygen concentration. Findings unveiled a consistent trend: both nanoparticle and NO_x formations exhibit a similar response to changes in input conditions. Specifically, as the input equivalence ratio was increased or the oxygen concentration decreased, a simultaneous reduction in the formation of these pollutants was observed. This suggests a common influence of these factors on both nanoparticle and NO_x formation. Additionally, the research highlighted a critical parameter in maintaining a self-sustainable stationary flame: ensuring that the iron particles remained relatively close together, with a maximum particle-to-particle distance of approximately 0.5 mm or a minimum total iron particle surface area of at least 0.02 mm² per mm³ volume burner for oxidizer oxygen concentrations ranging from 13.5 % to 21 %. These findings provide valuable insights for optimizing the utilization of iron powder as a suitable option for burning in combustion processes and in the iron energy carrier cycle, enabling good energy conversion while minimizing environmental impacts. Novelty and Significance Statement: This study includes the first-ever measurements of nanoparticles and NO_x formation during iron powder combustion at different input equivalence ratios and oxygen concentrations using a practical lab-scale burner. The concept can be adapted for commercial and industrial uses in heating and power. Furthermore, the findings of this study can be used to determine the optimum conditions for low emissions with a self-sustainable stationary flame during iron powder combustion, providing valuable insights into the combustion characteristics of iron powder and offering practical guidance for optimizing its combustion processes in the iron energy carrier cycle.