Behavior of nitrogen oxides in a lab-scale coal ammonia co-firing system

The objective of this study was to determine the ideal coal–ammonia (NH3) co-firing conditions to achieve carbon neutrality and suppress NOx formation. This paper describes the characteristics of NOx formation in NH3–coal co-firing experiments. NH3 co-firing experiments were performed under intensive and air-staged combustion conditions using a 5 kW fluidized bed reactor. Air-staged combustion and divided fuel-injection were effective in suppressing NOx formation during NH3 co-firing combustion. The minimum and maximum NO concentration observed during intensive and air-staged combustion was 70 ppm and 700 ppm, respectively. In addition, some NH3 slips were observed under an NH3 co-firing ratio of 20% or more; however, the reduction effect of NO was observed. The NO concentration increased to approximately 500 ppm under pure NH3 combustion. The simultaneous injection of fuel and oxygen under fuel-rich conditions generated NO and N2O. It increased rapidly under incomplete combustion conditions and increased in proportion to the concentrations of HCN and CO. NH3 co-firing was accompanied by the suppression of NO formation and reduction of N2O and CO2 if injected in consideration of the temperature and oxygen concentration. •Air-staged combustion is effective in suppressing NO formation during NH3 co-firing.•N2O has a linear proportional relationship with the concentration of CO.•NH3 slips were revealed in the co-firing ratio more than 20% based on calorific value.