[Objective

]

To achieve the goal of “dual carbon” and promote the low-carbon transition of power generation

ammonia-coal co-combustion has been recognized as one of the effective approaches for reducing CO

2

emissions from coal-fired power plants. However

due to the high nitrogen content of ammonia

ammonia co-firing may significantly increase NO

x

emissions. Moreover

the ammonia injection location and mixing mode inside the burner directly affect combustion efficiency

ignition characteristics

burnout performance

and pollutant formation. Therefore

it is essential to clarify the influence of ammonia injection strat

egies on combustion behavior and NO

x

formation mechanisms in swirl-stabilized pulverized-coal flames. [Methods

]

In this study

based on a 0.5 MW double-swirl burner test system

computational fluid dynamics(CFD) simulations were performed to investigate the effects of ammonia injection location and ammonia co-firing ratio on ignition performance

burnout rate

and NO

x

formation characteristics under stoichiometric conditions. Three ammonia injection configurations were considered

including central ammonia injection

primary-air ammonia injection

and secondary-air ammonia injection. Special attention was paid to the coupling effects of local flow structure

recirculation zone

mixing sequence

and NH

3

reaction pathways on combustion characteristics and NO

x

generation in the burner. [Results

]

The results show that

compared with the pure-coal condition

ammonia co-firing decreases the overall combustion temperature and significantly increases NO

x

emissions

whereas the extent of the increase strongly depends on the ammonia injection location. For primary-air ammonia injection(PA-20%)

NH

3

rapidly undergoes exothermic oxidation in the high-temperature recirculation zone near the burner outlet

which promotes volatile release and accelerates pulverized-coal ignition. However

this configuration also intensifies the initial oxygen competition and leads to a lower burnout rate. For secondary-air ammonia injection(SA-20%)

NH

3

enters the high-temperature oxygen-rich region earlier

resulting in the highest NO

x

formation

with the outlet NO

x

concentration reaching 4.86 times that of the pure-coal case. In contrast

central ammonia injection(CA-20%) achieves relatively low NO

x

emissions together with a comparatively high burnout rate. The high-momentum NH

3

jet penetrates the swirling shear layer and delays its mixing with pulverized coal and oxygen

thereby promoting NH

3

pyrolysis and NO re

duction reactions. Under this condition

the contribution of the NH

3

pyrolysis pathway reaches 4.40%

and the NO formation is reduced by about 51% compared with SA-20%. [Conclusion

]

The outlet velocity of central ammonia injection is a key parameter for regulating NH

3

reaction pathways. As the NH

3

jet velocity increases from 7.48 m/s to 8.31 m/s

the proportion of the pyrolysis pathway increases from 4.05% to 6.41%. These findings indicate that optimizing the ammonia injection location and jet parameters can simultaneously suppress NO

x

formation and improve burnout performance

thereby providing a theoretical basis for the design and optimization of ammonia-cofiring pulverized-coal burners.