Effects of operation parameters on NO emission in an oxy-fired CFB combustor

Oxy-fuel Circulating Fluidized Bed (CFB) combustion technology, a very promising technology for CO2 capture, combines many advantages of oxy-fuel and CFB technologies. Experiments were carried out in a 50 kWth CFB facility to investigate how operation parameters influence the NO emission in O2/CO2 atmospheres. The simulated O2/CO2 atmospheres were used without recycling the flue gas. Results show that NO emission in 21% O2/79% CO2 atmosphere is lower than that in air atmosphere because of lower temperature and higher char and CO concentrations in the dense bed. Elevating O2 concentration from 21% to 40% in O2/CO2 atmosphere enhances fuel-N conversion to NO. Increasing bed temperature or oxygen/fuel stoichiometric ratio brings higher NO emission in O2/CO2 atmosphere, which is consistent with the results in air-fired CFB combustion. As primary stream fraction increases, NO emission increases more rapidly in O2/CO2 atmosphere than that in air atmosphere. Stream staging is more efficient for controlling NO emission in oxy-CFB combustion than that in air combustion. Oxygen staging provides an efficient way to reduce NO emission in oxy-CFB combustion without influencing the hydrodynamic characteristic in the riser.