Effects of the tertiary air injection port on semi-coke flameless combustion with coal self-preheating technology

Abstract

A novel coal self-preheating combustion technology was adopted to generate high temperature gas-solid two-phase fuel. Experiments on flameless combustion of the two-phase fuel were conducted in a 30-kW coal self-preheating combustion test rig. In flameless mode, effects of the single and the multi levels tertiary air injection ports were discussed, and the flue gas compositions (NOx and CO) and temperatures along the axis of the down-fired combustor were analyzed. To visualize the combustion process, the flame images were captured. It is confirmed that flameless combustion of high temperature gas-solid two-phase fuel can be easily established, and (1) the temperature profile is uniform and it is transparent in the combustor; (2) NOx emission can be reduced about a half compared to other combustion modes; (3) for a single level tertiary air, NOx emission can be minimized by the proper injection port while NOx emission and CO emission might be increased by an inappropriate port; (4) for the multi levels tertiary air, NOx emission can be reduced further by moderate tertiary air injected in the reducing zone, and NOx might be increased while some tertiary air is injected in the burnout zone. It is clear that NOx and CO emissions can be controlled in a low level by rationally arranging two level tertiary air injection ports under flameless combustion.