Ammonia as a hydrogen carrier: LES of ammonia-solid fuel firing at varying air staging ratios

Hydrogen carriers, such as Ammonia (NH₃), is anticipated to be used as a carbon-free alternative for solid fuels, such as coal. Hence, the effect of air staging ratio (ASR) on emissions from NH₃ co-firing with sub-bituminous coal was numerically investigated in a small-scale coal combustor via a Large Eddy Simulation (LES) method. The validation with experimental data demonstrated a difference in nitrogen oxides (NO_x) and temperature profiles of less than 10 %. Carbon dioxide (CO₂) and sulphur dioxide (SO₂) levels are decreasing as the NH3 percentage rises, but ASR has minimal influence. Increasing the ASR from 20 to 60 % resulted in NO_x reduction, except for 60 calorific (cal.) % NH₃, where NO_x began to grow at ASR 60 %. In the said case, peak temperature was recorded in the over-fire Air (OFA) zone due to considerable unburned carbon (UC) oxidation, resulting in an increase in thermal NO_x. Due to oxygen deficiency, coal volatiles and NH₃ are thought to burn in the firing zone due to dominant devolatilization, resulting in significant UC/char oxidation in the OFA zone. Overall, with proper ASR tuning, NH₃ co-firing can produce low CO₂, SO₂, and NO_x, and existing coal-fired utility ASR technology can be used.