Numerical study of combustion characteristics for pulverized coal under oxy-MILD operation

• Oxy-MILD combustion of coal was numerically studied at varied oxygen concentration.
• Oxygen enrichment leads to higher combustion temperature and higher heat release under oxy-MILD operation.
• CO emission reduces with oxygen enrichment under oxy-MILD combustion.
• Oxygen enrichment enhances the fuel-NOX destruction under oxy-MILD combustion.

MILD (Moderate or Intense Low-oxygen Dilution) combustion is a novel technology to reduce NOX emission from combustion. With the development of this technology, it is expected to combine this technology with oxy-fuel combustion to jointly control the pollutants from fossil fuel combustion. The present paper investigates the combustion characteristics of coal under oxy-MILD operation with the aid of CFD simulations. A seven-step global reaction mechanism is used for modeling coal combustion involving gaseous volumetric reaction and particle surface reaction. The predicted results using the adopted models for the reference case agree well with the experimental results. It is revealed that, the combustion temperature level increases with the enhancement of initial oxygen concentration because of the reduced injection momentum and promoted heat release. The in-furnace CO formation increases but the final CO emission reduces when enhancing the oxygen concentration under oxy-MILD combustion. Moreover, oxy-MILD combustion shows a greater potential on NOX formation reduction than air-MILD combustion, and this potential is promoted at higher initial oxygen concentration.

The aim of this study was to investigate the different combustion characteristics of coal MILD combustion under air (O2/N2) and oxy-fuel (O2/CO2) atmospheres. The temperature and species distributions as well as NO formation are numerically compared. Oxy-MILD combustion of coal has shown greater potential on NO reduction than air-MILD combustion, and this advantage is promoted by enhancing the oxygen level in oxidizer due to larger CO release.Figure optionsDownload as PowerPoint slide