Effects of hydrogen–coal mixing on NOx formation during partial decarbonisation of rotary kiln iron ore induration - pilot-scale experiments using spectroscopy and video analysis

This pilot-scale study examines hydrogen–coal co-firing at 0–65% hydrogen energy substitution in a 580-kW furnace representative of industrial iron-ore kiln systems. Five burner families, comprising six tested configurations, varied the relative positions, injection directions and velocities of hydrogen, coal and primary air. Relative to the pure-coal case, outlet NO x decreased by 15–24% at 20% hydrogen substitution; at 40% substitution, the change ranged from a 5% reduction to a 31% increase; and at 60–65% substitution, NO x increased by 42–97%. The emission performance is associated with changes in fuel NO x and thermal NO x formation, supported by apparent coal-ignition distance, apparent line-of-sight temperature, plume structure and local oxygen availability.