Investigation of low-NOx strategies for natural gas combustion

Different NOx control techniques have been investigated and implemented in a natural gas burner at two different scales. Both fuel- and air-staging strategies can be implemented in a single burner, by properly adjusting some of the available settings. Experiments were performed on a semi-industrial scale (thermal input 0.3-0.33 MW) in a laboratory furnace. The study included a thorough parametric analysis to identify the optimum operating conditions for minimum NOx emission. In addition, some detailed in-flame measurements provided valuable information for the understanding of the relevant phenomena. In a second stage, a prototype of the burner was tested in a boiler (6.5-17 MW(t)) to check the validity of the conclusions obtained on the smaller scale. The tests demonstrated that the new burner can reduce NOx emissions by > 70% with respect to the values obtained with the burner originally installed in the same boiler. Comparison between the measurements performed on both scales also provided valuable information regarding the effects of scaling on the performance of low-NOx burners. A scaling law intermediate between the constant-velocity and residence-time criteria was selected in one of the test series, leading to a remarkable similarity of the results obtained on the two scales, in terms of both NOx emissions and qualitative burner performance. (C) 1997 Elsevier Science Ltd.