Effects of steam on the sulfation of limestone and NOx formation in an air- and oxy-fired pilot-scale circulating fluidized bed combustor

► Sulfation under oxy-fuel combustion is explored at bench and pilot scales. ► In the presence of steam, direct sulfation is slower than indirect sulfation. ► Calcium utilization for air-firing can be increased by steam injection. ► Steam decreases NOx emissions for both air- and oxy-firing modes. ► Steam should be considered in future bench- and pilot-scale combustion studies.