Combustion characteristic study with a flue gas internal and external double recirculation burner

Abstract

A new low NOx burner for gas boiler is designed. A hollow tube is embedded in the burner axial center line, which is combined with the flared flame stabilizer to draw back the internal flue gas from inside the boiler, and a flue gas recirculation tube is installed outside the boiler to draw back the flue gas from the end of the boiler. The effectiveness of the burner is evaluated by industry experiments and extensive computational fluid dynamics (CFD) simulations. The research results show that the excess air ratio and external flue gas recirculation (e-FGR) rate significantly alter the temperature distribution and NOx emission of the boiler. The temperature and NOx emission do not vary monotonically with the excess air ratios, but decrease monotonically with the e-FGR rates. To achieve the low NO emission, the optimum excess air coefficient α should be 1.15 due to the better temperature uniformity, and the value of e-FGR rate should be in the range of 28%–40%. In addition, the maximum concentration of NO does not appear on the flame surface, but in the downstream region of the flame.