Numerical simulation on flameless combustion in U-shaped radiant tube for continuous annealing furnace
XU Jia-qiang1, SONG Zhong-hua2, PAN Ni1, TAN Fang-guan1, XU Xue-cheng1, HE Zhu1
1. Key Laboratory for Ferrous Metallurgy and Resources Utilization of Ministry of Education, Wuhan University of Science and Technology, Wuhan 430000, Hubei, China; 2. Wuhan Iron and Steel Group Research Institute, Wuhan 430000, Hubei, China
Abstract：In order to ensure that the heated workpiece is evenly heated without affecting its surface quality,the metallurgical industry generally uses radiant tubes to indirectly heat the workpiece. But at the same time,due to the limited combustion space in the radiant tube,it is easy to produce a local high temperature zone,which will affect the quality of the heated product,and the high temperature will cause a large amount of NOx to be generated. In addition,the thermal stress generated by the large wall temperature difference will cause the tube wall damaged by creep,shortening its service life. Therefore,in order to optimize the performance of the radiant tube, a new type of radiant tube burner is proposed based on the flue gas recirculation technology,which can increase the flue gas circulation while ensuring continuous combustion. Specifically,the traditional combustion is first carried out in the radiant tube. After the temperature is higher than the auto-ignition point of the fuel,a large amount of flue gas is introduced,so that the U-shaped radiant tube reaches a flameless combustion state. At this time,the surface temperature is more uniform and the NOx emission is lower. Through the establishment of a mathematical model of the U-shaped radiant tube with the burner,supplemented by experimental verification,the flameless combustion characteristics in the U-shaped radiant tube were explored,including the combustion state in the radiant tube,the uniformity of surface temperature and the NOx emission,and the existing U-shaped radiant tube was compared and analyzed,and the influence of different smoke volume on the flameless combustion characteristics in the radiant tube was discussed. The research results show that the flameless combustion state is completely different from traditional combustion,under traditional combustion,there is an obvious local high temperature zone in the front of the radiant tube;with the introduction and further increase of the volume of cigarette smoking,the peak temperature continues to drop,and the high temperature zone. There is a phenomenon of transfer to the rear of the radiant tube. When the flameless combustion state is reached,the local high temperature area disappears;the flameless combustion greatly improves the surface temperature uniformity of the radiant tube,the extreme value of the temperature difference between the radiant tube wall is reduced from 110 K to 35 K,and the temperature uniformity coefficient is reduced from 9% to 2.9%,which is conducive to improving the actual temperature of the radiant tube. Service life;the emission of pollutant NOx is reduced,from the initial 0.022%to less than 0.000 1%.
徐家强, 宋中华, 潘妮, 谭方关, 许学成, 贺铸. 连退炉用U型辐射管内无焰燃烧的数值模拟[J]. 钢铁, 2022, 57(1): 143-150.
XU Jia-qiang, SONG Zhong-hua, PAN Ni, TAN Fang-guan, XU Xue-cheng, HE Zhu. Numerical simulation on flameless combustion in U-shaped radiant tube for continuous annealing furnace[J]. Iron and Steel, 2022, 57(1): 143-150.
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