Low-NOx Modification of a Heavy Fuel Oil Swirl Burner Based on Semi-Industrial Scale Experimental Tests

A proposed swirl burner was modified from a burner used in a 300 MWe oil-fueled power plant. In particular, burner construction, including expanded nozzles, swirl numbers, and air ratios were changed. Then, experimental tests were carried out in a semi-industrial test rig with a horizontal cylindrical furnace with a single-swirl burner. The thermal input of the furnace was 9 MW. The species concentrations of O2, CO, and NOx in the flue gas were measured. NOx emission with the original burner was 320 ppm (3 vol % O2). However, NOx emission decreased to 195 ppm (3 vol % O2) with the proposed burner during optimal operation. Through a series of adjusting experiments, a 35�39% abatement of the NOx emission from the single-burner test could be maintained when the original burner was replaced by the proposed one. NOx emission measured from a full-scale industrial furnace is approximately 341 ppm (3 vol % O2) under ordinary operating conditions. The predicted NOx concentration from the industrial furnace could achieve 207.8 ppm (3 vol % O2) employing the proposed swirl burner under optimal operating conditions. The flow fields (including the recirculation zone and turbulent intensity) downstream of the two burners were compared on the basis of the numerical results. A CCD image system was applied to capture the flame structure downstream of the burner. A mushroom-shaped flame structure was observed with the proposed burner, whereas a fan- shaped diffusion flame was observed with the original burner. A strengthened division in the flame was formed at the burner outlet with the proposed burner. Temperatures ranged from 1184 to 2114 °C downstream of the burner, which was determined through the two-color pyrometry method for each burner. The minimum temperature of the reference section was reduced by 154 °C, and the average temperature was reduced by 76.9 °C when the proposed burner was applied. The proportion of the temperature region higher than 1500 °C in the reference section was calculated. The initial proportion was 94.96%, which was reduced to 80.91% when the proposed burner was applied. This represents a decrease of 14.05% through the modification.