High-efficient combustion of gas-fired furnace with 21∼36% oxygen-enriched air

Abstract

This experimental investigation was aimed at studying the influences of 21∼36% oxygen concentrations on the heating rate, emissions and temperature distributions. In consideration of the actual needs, 1300 °C was selected for the heating temperature of flue gas. When the billet was taken out from furnace, the billet core temperature were about 1200 °C, and the temperature difference between the billet surface and core fluctuated between 10 to 50 °C. At the same time, in order to ensure the quality of billet and save energy and cost, the heating temperature and oxygen concentration in furnace should not be too high. Increasing the oxygen concentration led to higher heating rate due to lower level of the inert gas (N2) in the combustion air. When the oxygen concentration was increased from 21% to 36%, the heating rate of flue gas was increased by 68.3% in the heating test, and the heating rate of billet core was increased by 39.5%. Higher oxygen concentration yielded higher flame temperature. Hence, the NOxconcentration increased with increasing oxygen concentration. Moreover, the generation of NOxconcentration was faster and more under the excess oxygen at higher oxygen concentration levels. The NOxconcentration is very low and the highest NOxconcentration is only 27.2 ppm even at the highest oxygen concentration under flue gas cycle combustion conditions. Under the graded oxygen combustion and concentrated oxygen combustion conditions, the higher the oxygen concentration, the greater the difference in NOxemission concentration. The concentration of NOxin the graded oxygen supply is relatively low. Additionally, Numerical Simulations indicated that the temperature distributions became progressively nonuniform with increasing oxygen concentration because the absorption coefficient and convective heat transfer coefficient were altered.