N₂O Formation And Control In Circulation Fluidized Bed Boilers

The problems of N2O Emissions from Circulating Fluidized Bed were noticed for the strong Greenhouse effects of N2O. In a 135MW power plant N2O emissions testing, the greenhouse effects produced by CFB N2O emissions could quivalent to 16.2% of CO2 for most. With Climate Change in the world, N2O emissions will become a limiting factor for the development of CFB technology in the future.Many factors could affect N2O emissions in CFB, including temperature, oxygen concentration, Ca/S and air-staged. Bed temperature must be the first of these. But changing operating conditions in CFB could not solve the problem for their bad effects on SO2 and NOx emissions.N2O emissions from the fuel N, the conversion of fuel N to N2O could be a very complex process in combustion of coal, involving homogeneous and heterogeneous reactions. And both ways contained complicated mechanisms for N2O formation and decomposition. Experiment study for single particle coal combustion gave the conversion rate from fuel N to N2O and NOx, and also the conversion rate of volatile N and Coke N cenvers to N2O and NOx respectively.Nitrogen balances in CFB were totally different from single particle coal combustion. Conversion rate of fuel N to N2O in CFB was 3-4 times more than the same condition in single coal particles combustion. On the contrary, NOx conversion rate made only 1/4 comparing with a single particle of coal. These prove that the largest source of N2O emissions must be the reaction of coke with NO in CFB.Besides, it was found in CFB experiments that, air-staged can significantly reduce N2O emissions, the location of OFA must be the key factor. And, the effection of N2O reduction using reburning would apparent only if temperature higher than 950℃in CFB cyclone.