Combustion Using High Temperature and Low Oxygen Content Air and Technique Renovation of Traditional Gas-Fired Radiant Heating Tube

Combustion using high temperature and low oxygen content air is a new technique with many advantages such as larger energy saving and lower NO_x pollution. In this new technique, air is preheated over the self-ignition point of the fuel and the volumetric oxygen content in combustion chamber is less than 15%. It can be implemented by utilizing high efficient regenerative heat exchanger and recycling exhaust gas in furnace. In this research, experiments were conducted to investigate the flame characteristics using nitrogen as diluting gas and adopting electric heating element to preheat air. The results show that on the condition of high temperature and low oxygen content air, the volume, the brightness, and the color of flame change significantly, the maximum temperature of flame decreases obviously, and the temperature distribution in furnace becomes uniform. A technique renovation is proposed for traditional radiant heating tube based on this new combustion scheme, and the advantages obtained by this renovation are evaluated. It is found that higher heat efficiency, uniform surface temperature, longer life expectancy, and lower NO_x emission and combustion noise can be achieved. The calculation results show that the heat efficiency of radiant-tube can reach 85.3% and save energy up to 21.55% after the renovation. At the same time, the non-uniform coefficient of surface temperature is decreased to 0.02 or less. A small-scale test facility is being built to validate these results.