A model of the chemical pathways leading to NOx formation during combustion of mixtures of cellulosic and plastic materials

A numerical model has been developed to study the NOx formation during the combustion of mixtures of cellulosic and plastic fuels within a fixed bed reactor. The model simplifies the flow to a one dimensional succession of about 1000 perfectly stirred reactors (PSR) and includes a detailed chemical model that computes 113 species involved in 893 reversible reactions, to detailed the reactive path of NOx formation. The calculations use the PSR model included in Chemkin II. The solid phase is not solved but instead the input species are generated from an experimental degradation study of the fuel. Nitrogen oxide (NO) is studied as the primary component of NOx. The model has been validated in past publication by comparison of the results with experimental measurements. The model has then been used to investigate the mechanisms of formation and destruction of the NO during the combustion process of municipal solid waste. Numerical results show that NO forms rapidly from the oxidation of intermediary species such as NCO, HNO and NH that originate from the fuel pyrolysis. NO consumption occurs primarily through reactions with NHi and NCO leading to the formation of N2. The ultimate formation and consumption of NO depends mostly on the primary air flowing through the fuel bed with a minimum being observed when primary air and fuel are present in proportions close to stoechiometric.