REDUCTION OF N2O BY GAS INJECTION IN CFB BOILERS

An investigation has been conducted into the possibilities of reducing N2O emissions from circulating fluidised-bed (CFB) boilers, by means of fuel-gas injection in the cyclone. Calculations assuming homogeneous chemistry indicate N2O reductions of 90% or more when methane is injected. Full-scale experiments in a CFBB of 12 MW have verified the feasibility of N2O reduction by gas injection without any additional air; the reduction level, however, was in the region of 50%, compared with calculated values of about 90%. This difference can be attributed to heat loss to the particles in the cyclone, and to the walls. Gas injection did not cause any significant rise in NO emissions, and no hydrocarbons were emitted except when the excess air approached zero. The CO emissions fell when gas was injected.