Experimental evaluation of ammonia injection strategies for different solid fuel types in drop tube furnace for carbon-free energy transition in thermal power plants

Ammonia, known for its high hydrogen content and favorable storage properties, is emerging as a key carbon-neutral fuel for the global energy transition. South Korea aims to demonstrate the application of ammonia in existing coal-fired power plant boilers by 2027, targeting a reduction in CO₂ emissions. However, research in this area is crucial because the combustibility and exhaust gas composition, which are vital for power plant operations, may change. This study investigates the impact of ammonia injection position and coal grade on combustibility and exhaust gas in coal-fired power plants using an ammonia drop tube furnace (ADTF). Experimental results indicate that ammonia injection position significantly influences combustibility and exhaust gas. Sub-bituminous coal (Coal B), with higher volatile matter content, exhibited enhanced combustibility and lower unburned carbon (UBC) emissions compared to bituminous coal (Coal A). NOx emissions were significantly reduced when ammonia was injected downstream because of its function as a reducing agent. Particularly for coal B, when injected at the lowest position, it exhibited a lower emission (91.74 ppm) compared to the complete combustion of the coal (123.82 ppm). The combustion trends of mixed coal resembled those of Coal A; however, it presented a viable approach for enhancing high-grade coal utilization and demonstrated superior emission characteristics in certain respects compared to single coal. These findings demonstrate the potential of ammonia-coal co-firing to reduce CO₂ and NOx emissions in coal combustion while improving boiler combustion efficiency. Such insights are expected to significantly contribute to the demonstration project of ammonia-coal co-firing power generation.