Enhanced NOx reduction performance in the I-type radiant tube by combining a novel triple air-staging with flue gas recirculation

Abstract

In this study, a novel triple air-staged combustion (ASC) with internal flue gas recirculation (FGR) was proposed to further achieve low NOx emissions and high combustion efficiency in the I-type radiant tube (RT). The effects of air vent structural parameters, including secondary air vent gap d (0, 1, 2, 3 mm) and diameter D (2, 4, 6, 8 mm) of tertiary air vents, on NOx emission and thermal efficiency were analyzed by numerical simulation. The results showed that NOx emissions increased from 33.7 to 66.0 mg/m3 as the secondary air vent gap changed from 0 to 3 mm. The thermal efficiency was higher than the original structure only at d=3 mm. When the tertiary air vent diameter increased from 2 to 8 mm, NOx increased from 49.3 to 180.4 mg/m3 and the thermal efficiency changed with a slight variation. On the premise of higher thermal efficiency than the original structure, the NOx at D=2 mm reached the minimum value of 49.3 mg/m3 under all optimized schemes, with a 64.0% reduction.

Keywords

• Radiant tube
• Triple air-staged combustion
• Internal flue gas circulation
• NOx emissions
• Thermal efficiency