Numerical simulation of the combustion characteristics and NOx emission of a swirl burner: Influence of the structure of the burner outlet

• The prediction shows a good agreement with experimental results.
• Burner performance increases as primary air cone length decreases.
• Burner NOx reduction capacity increases as inner secondary cone length increases.
• Burner performance increases as outer secondary air cone length increases.

Numerical simulations on coal combustion and NOx emissions were performed for a centrally fuel-rich pulverized-coal swirl burner. By varying cone lengths of primary air, inner secondary air and outer secondary air, the burner outlet structure effect was disclosed in detail. The new findings which can deepen the understanding of the swirl burner performance are as follows. The ignition performance and NOx reduction capacity of burner increases as primary air cone length decreases. As the inner secondary air cone length increased, ignition performance of burners becomes poor and the NOx reduction capacity increases. The ignition performance and NOx reduction capacity of burners become stronger with increases in outer secondary air cone length. Under the conditions including that (i) outer secondary air cone length is three times of the outer secondary air duct diameter, (ii) inner secondary air cone length is 50–100% of outer secondary air cone length and (iii) primary air cone length is 0 mm, the burner presents an excellent performance on NOx emissions and pulverized-coal combustion characteristics with air-staging conditions.