Reduction of N2O emissions from fluidized bed combustion with afterburning

One way to reduce N2O emissions is to raise the temperature of the combustion gases. This can be done in the combustion chamber during conventional operation of a boiler, but also through injection of a secondary fuel, preferably in a separate combustion chamber. This paper reports investigations made at the 12 MW circulating fluidized bed boiler at Chalmers University of Technology, where in the absence of a separate combustion chamber, secondary fuel was injected into the primary cyclone. While the gas temperature was increased in the cyclone normal operation conditions were maintained in the combustion chamber. A number of injection fuels were used, including Liquid Petroleum Gas, pulverized coal and pulverized wood. The reduction of N2O was shown to be independent of tbe fuel used and only a function of !be temperature achieved. Almost all N2O could be removed by a temperature increase of about 150°C under otherwise normal conditions in the fluidized bed combustor. The other emissions were not increased by the fuel injection. On the contrary, the NO and CO emissions were reduced. Sulphur capture was not affected by the temperature rise. in the cyclone. The behaviour of the cyclone as a separate combustion chamber and the burning characteristics of the different injection fuels are discussed