Hydrolysis of HCN as an important step in nitrogen oxide formation in fluidised combustion. Part 1. Homogeneous reactions

The formation of nitrogen oxides at conditions of fluidised combustion was investigated by the combustion and hydrolysis of HCN, the main precursor of nitrogen oxides. The experiments revealed that an understanding of the complex conversion mechanism of fuel-N during coal combustion could be simplified by concentrating on the conversion of HCN. There are two main parallel conversion routes. The oxidation of HCN via NCO to nitrogen oxides and alternatively its hydrolysis first into NH3 and subsequent oxidation. Gaseous SO2, the concentration of which is controlled in FBC by limestone, interacts as well with fuel-N intermediates leading to a suppressed formation of NO while favouring N2O formation. Finally it becomes clear that the parallel formation of NH3 by hydrolysis not only leads to an additional formation of NO at medium temperatures but also to an additional decomposition of NO at elevated temperatures.