Hydrolysis of HCN as an important step for the conversion of fuel-N

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 understanding of the complex conversion mechanism of fuel-N during coal combustion can be simplified by concentrating on the conversion of HCN. There are two main parallel conversion paths. The oxidation of HCN via NCO to nitrogen oxides and, alternately, first its hydrolysis into NH3 and subsequently the oxidation. In the presence of Ca-compounds CaCN2 is an intermediate product that directs the fuel-N conversion towards the formation of NH3 which is subsequently oxidised to NO. The catalysed hydrolysis of HCN forms, besides its relevance for nitrogen oxide formation, also an explanation for the observed favoured release of NH3 during pyrolysis of low rank coals such as lignites.