Numerical modelling of ammonia-coal co-firing in a pilot-scale fluidized bed reactor: Influence of ammonia addition for emissions control

Abstract

The co-firing of coal and NH3 is a sustainable solution allowing the retrofitting of coal power facilities without major modifications while contributing to global decarbonization goals. However, the use of NH3 for power generation still presents some research gaps. This study delivers a 2D Eulerian-Lagrangian numerical model describing the co-firing of coal-NH3 in a pilot-scale fluidized bed reactor. The numerical model is validated against experimental data on coal combustion to assess the accuracy of the model·NH3 co-firing ratio is varied between 0 and 80% (by mass) and the effect on the combustion process is broadly investigated to determine the impact on heat release, and carbon, NO, and NH3 emissions. The effect of NH3 injection position into the reactor and air staging on NO formation is studied. Also, the impact of NH3 on the reactor temperature distribution and radiative flux is evaluated. Results indicate that NH3 co-firing delivers CO2 emissions decrease of up to 26% compared to pure coal firing. For a co-firing fraction of 10% NH3, NO emissions level was identical to that of coal firing alone, yet between 20 and 80% ratio NO emissions gradually decreased by up to 40%. The NH3 injection location had a substantial effect on NO emissions, with injection points further downstream the bed surface leading to increased NO concentrations. Air staging also proved to have a dominant effect on NO formation, with a 50% reduction of NO emissions obtained for a 20% air staging alone. Lower gas temperatures and decreased radiative flux were predicted as the NH3 ratio increased. Given the similar heat transfer rates measured between 10 and 20%, a 20% NH3 operation would be possible without a detrimental effect on temperature and radiative flux.