Experimental Study Of Fuel N Conversion In Oxy-Coal Combustion

The global warming is becoming more and more severe in this century, which is believed to be the result of a strengthening of the greenhouse effect caused by large tons of CO₂ emission. CO₂ is generated by the fossil fuel burning, in which pulverized coal power plant is one of the biggest contributors. As one of the most promising technologies, oxy-fuel combustion technology can achieve CO₂ and NO simultaneous reduction during coal combustion. In this technology, pure oxygen and part of recycled flue gas will take part in the combustion instead of air.In this paper, the conversion characteristics of volatile nitrogen and char nitrogen to NO was studied, in which some aspects that affect the fuel nitrogen conversion and recycled NO reduction were discussed, which provides theoretical understanding for the application of oxy-fuel combustion. The char samples were produced in the simulated oxy-fuel combustion flue gas on SHEFR and were then analysed by TGA. And CH₄/NH₃ ratio was derived from the calculation of FG-DVC. DTF was used to investigate the NO emission by separating volatile and char combustion. The effects of O₂/CO₂ ratio, excess oxygen ratio, CH₄/NH₃ molar ratio and temperature on the volatile nitrogen and char nitrogen conversion were discussed. The interaction between the fuel nitrogen and recycled NO was also studied and summuried.The results indicate that in reducing atmosphere, volatile-N conversion is very low no matter how much other parameters change, such as temperature, O₂/CO₂ or CH₄/NH₃. Increasing of temperature will enhance generating NO, but has little effect on reducing recycled NO. As CH₄/NH₃ ratio increasing volatile conversion ratio decreases while NO concentration increases. Volatile nitrogen conversion decreased if recycled NO increases and NO concentration decreases with recycled NO increasing.The experimental results of bituminous char and anthracite char show the effect of temperature on recycled NO reduction is negligible. In oxidizing atmosphere, as temperature increases, the bituminous char-N conversion increases. However, it has little influence on the anthracite char-N conversion. In reducing atmosphere, temperature increasing suppresses the fuel nitrogen conversion. As recycled NO increasing, fuel nitrogen is being reduced. When recycled NO is 950ppm, as char particle size increases, the effect of recycled NO on the fuel-N conversion is significant. In different O₂/CO₂ atmosphere, different kinds of chars have different kinds of fuel nitrogen conversion. And the effect of char particle size on fuel-N conversion in oxidizing and reducing atmosphere is opposite.