Impact of OFA on combustion and NOx emissions of a large-scale laboratory furnace fired by a heavy-oil swirl burner

Abstract

Experiments were carried out on a horizontal test furnace to assess the overall air-staging combustion performance and NOx emissions of a large-scale laboratory furnace fired by a heavy-oil swirl burner. Impacts of over-fire air (OFA) parameters (including the OFA position and ratio) on NOx and CO emissions were experimentally and numerically evaluated in the test furnace. The experimental results indicated that both the OFA ratio and positioned location affected NOx emissions during the heavy fuel oil (HFO) combustion. For the OFA positioned location downstream from the burner nozzle outlet, it was found that a relatively larger distance between OFA and the burner outlet could generate lower NOx emissions and almost yield no increase in the burnout loss. A high-temperature region above 1773 K was obtained in a downstream reference section of the burner jet and introducing OFA shrank significantly the high-temperature region. Additionally, industrial-size measurements performed in an industrial furnace were used to confirm further OFA impacts. In the industrial furnace, a 20% OFA ratio application (the primary combustion equivalence ratio of 0.88) reduced NOx emissions from 540 to 420 mg/Nm3 at 3% O2; this NOx reduction proportion (i.e., 22.22%) was close to levels determined in lab-scaled experiments.