Establishing a low-NOx and high-burnout performance in a large-scale, deep-air-staging laboratory furnace fired by a heavy-oil swirl burner

• Developing a low-NOx heavy-oil combustion configuration.
• Trialing the combustion configuration in a large-scale laboratory furnace.
• Evaluating combustion and NOx emission characteristics under various conditions.
• Establishing an optimized low-NOx and high-burnout performance.

A combustion configuration consisting of a low-NOx heavy-oil swirl burner along with overfire air (OFA) and flue gas recirculation (FGR), was developed for the low-NOx heavy oil combustion in a lab-scale furnace. Combustion experiments were performed with various heavy-oil supply temperatures, different oil spray nozzle types, and with or without feeding FGR. The combustion configuration was found to achieve low NOx and acceptable CO emissions (levels of 240–286 mg/m3 and 45–175 mg/m3 at 3% O2, respectively), even under the conditions without FGR. Increasing the FGR ratio from 0 to 10% attained a NOx reduction of 9% without an obvious increase in CO emission. In the oil atomizing nozzle type aspect, a radial bias pattern, which was designed to lower NOx emissions and improve ignition by regulating fuel bias combustion, actually resulted in higher NOx and CO emissions than those using a uniformly atomizing pattern. Decreasing the heavy-oil supply temperature (from 154 °C to 132 °C) prolonged the fuel combustion process and reduced NOx emissions. Finally, the optimized operation with low NOx and CO emissions (240 mg/m3 and 45 mg/m3 at 3% O2, respectively) was established.