Formation of nitrogen oxides in rotary kiln burners: an assessment of pilot scale experiments using gaseous, liquid and solid fuels

The combustion process in rotary kilns for iron ore production is associated with high temperatures and large amounts of highly preheated air (λ=5-6). These conditions are favourable for NOx formation. Further, coal is typically the main fuel in the process and the CO2 emissions need to be reduced. Thus, emission control strategies are becoming of increasing importance for this type of industrial processes. The present work studies the formation of NOx during combustion of oil, gas, two coals and different blends of coal and biomass. The paper includes both experimental and modelling work. The experiments were performed in co-operation with LKAB using their pilot scale burner test facility (400 kWfuel), which is able to simulate the conditions of the full-scale process. The model, which is used to interpret the experimental results, is based on detailed reaction kinetics with simplified descriptions of temperature and mixing profiles. The results show that oil and gas flames lead to significantly higher NOx formation than solid fuel flames. In general, the thermal formation route is shown to be an important contributor to NOx formation, i.e. also for the solid fuels