The experimental study on nitrogen oxides and SO2 emission for oxy-fuel circulation fluidized bed combustion with high oxygen concentration

• Oxy-fuel CFB combustion with flue gas recycle at an overall O2 concentration of 50%.
• The nitrogen oxides and SO2 emission were studied.
• A lower secondary flow ratio improves the sulfur capture efficiency.
• Oxygen staging combustion is a new and safe mode for oxy-fuel combustion.

Oxy-fuel circulating fluidized bed combustion (CFBC) has an advantage of being operated with high oxygen concentration, making it a better choice for CO2 capture. In order to study the emission of nitrogen oxides and SO2 under O2/RFG (recycle flue gas) firing mode with an overall O2 concentration of 50%, oxy-fuel combustion experiments with Datong coal were carried out in a 0.1 MWth oxy-fuel CFBC apparatus. The effects of different operating conditions on gaseous pollution emission, including gas staging combustion, oxygen staging combustion, and excess oxygen ratio were investigated. The experimental results show that a lower secondary flow ratio improves the sulfur capture efficiency, although the fuel N conversion increases slightly. Oxygen staging combustion, which means decreasing the oxygen concentration in the primary flow and increasing it in the secondary flow, is a new and safe method for oxy-fuel combustion with high oxygen concentration. A reasonably low excess oxygen ratio for the oxy-fuel CFBC operation is beneficial to simultaneously enable a decrease in the fuel N conversion and an improvement in the sulfur capture efficiency.