| The main primary energy of China is coal. Coal combustion provides essential thermal energy and electric supply for human beings, however it causes serious environmental issues, and Nitric Oxides (NOx) released from coal combustion is one of the main pollutants in China. Compared with the traditional combustion modes, flameless combustion technology has many advantages such as efficient radiative heat transfer, uniform temperature field distribution, low CO and NOx emission and quiet, and it has been widespread concerned by scholars.It was also defined as a new combustion method by the international combustion institute. However, research on pulverized coal flameless combustion is very limited and it still needs further study. In this paper, the combustion characteristics and emission characteristics of pulverized coal flameless combustion were established by numerical simulation and experimental study, which benefit for further theoretical and practical development of pulverized coal flameless combustion.Datong bituminous, Yimin lignite and Xinjiang Saier coal were selected as samples as they were three kinds of coals. The influence of the combustion atmosphere, furnace temperature, O2concentration and gas flow on the combustion and NO emission characteristics in conditions of high temperature and low oxygen concentration were researched in a horizontal tube furnace. The results show that compared with O2/N2and02/Ar, the NO emission in O2/CO2atmosphere is less than half of that in the other two atmospheres, and it is believed that the large amount of CO increased by high concentration of CO2is the dominant factor for the NO reduction. The rise of furnace temperature accelerate the release of N, however, when the temperature increase to1300-1350K, the NO emission decreases. The oxidizing reaction of N is inhibited and the corresponding NO emission is low when the O2concentration is below10%, while the corresponding NO emission grows rapidly when the O2concentration ranges from10%to21%. In addition, the nitrogen content, FC/V value and volatile content have significant influence on the N conversion and NO emission. Also, based on the reviewing and summerizing the design of flameless combustion furnace which used pulverized coal, sawdust and natural gas as fuel, this paper preliminarily designed and verified the structure of pulverized coal flameless combustion furnace. Finally, the influence of combustion atmosphere, preheating temperature, O2concentration and jet velocity on the combustion characteristics of pulverized coal flameless combustion were studied by numerical simulation. The simulated results indicate that O2/CO2atmosphere can achieve low NOx emission and uniform temperature distribution. Higher preheating temperature enhances the entrainment effect, increases the uniformity of temperature field and NOx emission. Lower O2concentration improves the uniformity of temperature distribution and strengthen the entrainment rate, in the meanwhile, it reduces the NOx release. Higher jet velocity increases the entrainment rate to a large extent, while it may cause incomplete combustion. NOx emission of conventional combustion is75.45mg/MJ in a similar furnace, while it can reach27.33mg/MJ in this furnace. On the whole, flameless combustion can improve the uniformity of temperature distribution and the entrainment rate, reduce the peak temperature and the release of NOx and CO. |
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