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

Abstract

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 SO 2, N 2O, NO/NO x 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 SO 2 emissions, limestone addition at either position always results in decreases in N 2O and CO emissions and increases in NO/NO x emissions. Although the SO 2 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 N 2O and CO emissions but also greater increases in NO/NO x emissions than limestone addition at the bottom of the riser. A relatively small N 2O reduction (20% or less) together with associated increases in NO/NO x emissions lead to the conclusion that limestone addition at either of the positions is not an effective method for reducing N 2O emissions from circulating fluidized bed combustors.