Effects of Oxygen Staging and Excess Oxygen on O2/CO2 Combustion with a High Oxygen Concentration in a Circulating Fluidized Bed

To investigate the effects of oxygen staging and excess oxygen on combustion performance and gaseous pollutant emission, oxy-fuel combustion experiments with Datong coal were carried out in a 0.1 MWth oxy-fuel circulating fluidized-bed combustion (CFBC) apparatus under an O-2/CO2 atmosphere with a total O-2 concentration of 50%. The resulting CO2 concentration was higher than 90% in the flue gas under most experimental conditions. In oxy-fuel combustion, oxygen-staging combustion is a new, effective, and safe method for improving coal combustion performance, although flow-staging combustion remains effective. CO initially increased and then decreased, while SO2 and NO decreased, with an increasing oxygen concentration in the primary flow. The SO2 concentration increased, while NO decreased, with an increasing secondary flow ratio. Thus, the excess oxygen ratio is an important factor on oxy-fuel combustion. A higher excess oxygen ratio improves coal combustion efficiency and inhibits SO2 emissions while increasing NO emission.