On the Role of Limestone in the Conversion of Fuel-N in Fluidised Bed Combustion of Coal

摘要

Limestone addition in fluidiscd bed combustion of coal is a well established technique for sulphur dioxide control. However, calcium oxide interferes with fuel-N conversion by enhancing the NO emission while strongly reducing N_2O release. In laboratory experiments, the role of Ca-compounds on combustion of HCN was studied. It could be shown that CaCN_2 is an intermediate product that directs the fuel-N conversion towards the formation of NH_3 which is subsequently quickly oxidised to NO. Gaseous SO_2, the concentration of which is controlled in FBC by limestone, interacts as well with fuel-N intermediates and suppresses the formation of NO while favouring N_2O formation.