TED-AJ03-400 Radiation Reabsorption Effects on NO Emission from High-Temperature Air/CH_4 Counterflow Diffusion Flames

概要

論文の詳細を見る
To overcome the conflict between energy saving and pollution reduction, a new technical form of combustion called "High-Temperature Air Combustion Technology (HiCOT)" was proposed in Japan, in which the fresh airflow is heated over 1100 K through a heat exchanger and diluted by circulation of exhaust gas simultaneously. The applications of HiCOT to industrial furnaces have shown that this new technology has advantages of not only high efficiency but also low NO_x emission. Although lower NO_x emission has been achieved in real industrial furnaces, the fundamental mechanism of low NO_x emission has not been clearly understood. For the high temperature air combustion, since there is a great amount of radiative species such as CO_2 and H_2O in recirculated exhaust gas, the radiation and radiation reabsorption are suggested to have an important influence on NO_x emission. Because the gas radiative properties strongly depend on the wavelength, the no-gray radiation model is needed to correctly calculate the gas radiation in this kind of flame. However, almost all the previous studies have adopted the optically thin model without considering reabsorption to evaluate the radiation heat loss. Therefore, in this study, the radiation reabsorption effect on NO emission from high-temperature Air/CH_4 counterflow diffusion flames were numerically investigated by using the detailed chemistry. The radiation heat loss was calculated by using a statistical narrow-band model combined with the discrete ordinate method. The effects of radiation and reabsorption on NO emission with varying some flame characteristics such as temperature of preheated oxidizer, stretch rate of flame, CO_2 and the O_2 concentrations in oxidizer and the exhaust gas recirculation rate as well were clarified. The radiation and reabsorption effects on NO emission become significant and important as the temperature of the oxidizer increases and the flame stretch rate decreases. The increase of CO_2 concentration and decrease of O_2 concentration in gas mixture caused by exhaust gas recirculation further enhance these effects. From this study, it is found that radiation and reabsorption play a very important role in creation of the uniform temperature distribution in HiCOT. The absorption zone on the fuel side and the emitting zone on the high temperature oxidizer side that both increase with increasing oxidizer temperature and exhaust gas recirculation contribute to spreading the reaction region and flatting the temperature distribution. Although NO emission greatly increases with increasing preheated temperature of oxidizer, it is numerically demonstrated that low NO emission can be indeed achieved in HiCOT by means of allowing high stretch rate, the lower O_2 concentration, and the increasing heat capacity of gas mixture and radiation heat loss enhanced with increase of CO_2 concentration in gas mixture.
一般社団法人日本機械学会の論文

TED-AJ03-400 Radiation Reabsorption Effects on NO Emission from High-Temperature Air/CH_4 Counterflow Diffusion Flames

スポンサーリンク

概要

著者

関連論文

スポンサーリンク