Modelling of process heaters fired by natural gas

There is an increasing demand for ultra-low NO x burners-for example in the direct drying of foodstuffs. Gas-fired process heaters have been developed for such applications, and generally they consist of fuel-lean pre-mixed flames burning in a stream of ducted air. These flames produce NO x in large proportions by the prompt-NO route, and the correct prediction of NO x in these complex low-temperature flames by CFD methods requires the use of very accurate correlation equations. A method for achieving this is presented; it gives results in accordance with experimental observation. A study of the chemical mechanisms involved in the formation of NO is also presented. Also discussed is the formation of NO 2 from the NO, and of PAH in these burners