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Effects of staged oxygen on NOx formation and ash deposition characteristics during oxy-fuel combustion of high-alkali coal

2022 No. 04
689
629
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Authors:
SUN Ruijin
WANG Chang′an
ZHAO Lin
WANG Chaowei
MA Chengguo
CHE Defu
Unit:
State Key Laboratory of Multiphase Flow in Power Engineering,Xi′an Jiaotong University;Black Dragon New Double Stock Co.,Ltd.,
Abstract:

Zhundong coal is rich in reserves,but its high contents of alkali and alkaline earth metals can result in serious fouling on the heat exchange surface,influencing the boiler efficiency and the safe operation. Oxy-fuel combustion is promising to realize the clean utilization of Zhundong coal,and the oxy-fuel combustion under staged condition can further decrease NOx emission,while it affects the evolution of mineral in coal as well. There is little research on the effect of staged oxygen on ash deposition caused by high-alkali coal,and the possible relationship between NOx formation and ash deposition remains unclear. The characteristics of NOx formation and ash deposition under oxy-fuel combustion with staged oxygen were studied via a two-stage furnace. The experimental results show that the NO concentration in flue gas under oxy-fuel condition is much lower than that in air. The NO concentration in oxy-fuel atmosphere is about 80×10-6,while the NO concentration in air exceeds 170×10-6. Under the same O2 volume fraction (21%),the ash deposition propensity under oxy-fuel condition is also weaker than that in air,which is 26.20 mg/g and 16.45 mg/g,respectively. The results indicate the superiority of oxy-fuel combustion. With the increase of oxygen content in the main combustion zone (25%-60%),the conversion ratio of fuel nitrogen and ash deposition propensity of Wucaiwan coal both gradually increases. The overall structure of ash deposit is more compact,the agglomeration and adhesion between the accumulated ash particles are serious,the number of independent ash particles is significantly reduced. In addition,the pits on the particles surfaces develope,with more pore structures and more serious sintering observed. This reseach helps to better understand the ash deposition and NOx formation characteristics during the oxy-fuel combustion with oxygen staged,which is also conducive to accelerating the safe and clean utilization of high-alkali coal.

Keywords:
oxy-fuel combustion
staged oxygen
high-alkali coal
NOx formation
ash deposition
Citation format:
孙瑞金(1996—),男,江苏徐州人,硕士研究生。E-mail:934455245@qq.com
通讯作者:王长安(1986—),男,山东日照人,教授,博士。E-mail:changanwang@mail.xjtu.edu.cn
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