The influence of limestone addition at different positions on gaseous emissions from a coal-fired circulating fluidized bed combustor

This paper investigates the influence of Limestone addition at two different positions in the riser, one at the bottom of the riser and the other above the secondary air injection ports, on SO2, N2O, NO/NOx and CO emissions from a coal-fired circulating fluidized bed combustor with a riser of diameter 161 mm and length 6.2 m. In addition to reducing SO2 emissions, limestone addition at either position always results in decreases in N2O and CO emissions and increases in NO/NOx emissions. Although the SO2 emission is almost independent of the limestone injection position, the small difference in the effects, on the other gaseous emissions, of limestone addition between two injection positions is noticeable. Limestone addition above the secondary air injection ports results in larger reductions in N2O and CO emissions but also greater increases in NO/NOx emissions than limestone addition at the bottom of the riser. A relatively small N2O reduction (20% or less) together with associated increases in NO/NOx emissions lead to the conclusion that limestone addition at either of the positions is not an effective method for reducing N2O emissions from circulating fluidized bed combustors. (C) 1998 Elsevier Science Ltd. All rights reserved.