Computational Study on Cocombustion Characteristics of Pulverized Coal Blending with NH3 under Moderate or Intense Low- Oxygen Dilution Combustion Mode

Cocombustion technology of pulverized coal blending with NH3 has a promising use in large-scale CO2 reduced emission. However, the unstable flame and high NOx emissions during the cocombustion process retard its wide application. In order to overcome these limits, a new scheme of advanced moderate or intense low-oxygen dilution (MILD) combustion technology implemented in pulverized coal/NH3 cocombustion is proposed in this work, and a numerical study on cocombustion characteristics of pulverized coal blending with different NH3 proportions (0% similar to 50% NH3, by caloric) is performed. Results show that the achievement of a pulverized coal/NH3 MILD combustion regime is preferred at a high NH3 case. As NH3 proportions increase from 0 to 50%, the furnace temperatures are decreased due to the enhancement of heat transfer between flue gas and the furnace wall. The ignition time and temperature of coal particles are decreased by 52.1 and 33.0%, respectively, while the particle burnout time is prolonged by 52.3% and the char consumption rate decreases linearly. In addition, MILD combustion shows a good potential to reduce NOx conversion during pulverized coal/NH3 cofiring. Although the proportion of NH3 reaches up to 50%, NOx conversion ratio is only 2.1%. These results are expected to provide several new insights into stable flame and low NOx emissions of pulverized coal/NH3 cocombustion.

Automated summary

This study proposes an advanced moderate or intense low-oxygen dilution (MILD) combustion technology for pulverized coal/NH3 cocombustion to overcome the issues of unstable flame and high NOx emissions. The results show that a high NH3 proportion is preferred for achieving a pulverized coal/NH3 MILD combustion regime, leading to decreased furnace temperatures and improved heat transfer. Furthermore, MILD combustion has the potential to reduce NOx conversion during pulverized coal/NH3 cofiring.