Configuring hydrogen lancing to reduce carbon and nitrogen oxides emissions from coal-fired rotary kilns

Coal replacement with hydrogen is a strategy for reducing carbon emissions from high-temperature industrial processes. Hydrogen lancing is a direct way for introducing hydrogen to existing coal-fired kilns. This work investigates the effects of hydrogen lancing on nitrogen oxides (NO x ) emissions and ignition behaviour in a pilot-scale furnace that employs a 30 % coal replacement with hydrogen lancing. The investigation encompasses the impacts of lancing distance, angling, and velocity. Advanced measurement techniques, including spectrometry and monochromatic digital cameras, characterise the flame and assess emissions. The results indicate that the 30 % coal replacement by hydrogen lancing enhances combustion and reduces the emissions of carbon monoxides (CO). The flame characteristics vary with the location of the hydrogen injection, generally becoming more-intense than during coal combustion. NO x emissions during lancing are similar or up to double the emissions observed for pure coal combustion, depending on the lancing configuration. Increasing the distance between the hydrogen lance and coal burner increases NO x emissions. • Implementation of a hydrogen lance improves the ignition and combustion processes. • Hydrogen addition location can give up to double the level of NOx formation. • Close hydrogen injecting to the coal flow gives a lower level of NO x . • A bright flame with a clearly defined centre is associated with lower outlet NO x . • A higher wall temperature reduces the difference in flame characteristics between co-firing and pure coal flames.