On Ammonia-Blended Coke Oven Gas (COG) in Coaxial-Flow Nonpremixed Flame for Decarbonization

Coke oven gas (COG) is a promising byproduct gas generated in steelmaking processes because of its high heating value and large production volume. The large amount of hydrogen in COG contributes to combustion reactivity, flame stability, and decarbonization. Recently, a strategy for recycling COG cofired with other fuels has been proposed to support continued utilization. Ammonia is an attractive carbon-free fuel, a suitable candidate for cofiring with COG. In this study, the combustion and emission characteristics of ammonia-blended COG were investigated using a coaxial-flow nonpremixed combustor. Experiments evaluated the flame length, blow-off limit, and OH radical and NOx emissions. 2D simulation using ANSYS Fluent analyzed flame temperature and NO mole fraction. As a result, it was found that the flame length decreased with increasing ammonia blending ratio because of the reduced heat release rate and fuel reactivity. The normalized correlation based on Roper’s equation accurately predicts the flame length of COG, implying that COG can subsequently be interpreted as a general-purpose fuel. In addition, despite decreased blow-off limit of the ammonia-blended COG, it still maintained a significantly higher stability limit than methane due to the high hydrogen content of COG. OH-PLIF measurements revealed that the flame structure and reaction intensity were only slightly affected by ammonia blending, demonstrating the feasibility of ammonia-blended COG for stable combustion. NOx emissions increased substantially because of enhanced fuel-NO formation. This study provides a fundamental database for ammonia-blended COG under nonpremixed conditions and can contribute to the development of low-carbon industrial combustion systems.