Catalytic combustion of coal using alkali and transition metals loaded on iron ore oxygen carrier
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摘要: 煤气化反应是煤化学链燃烧过程的控制步骤,其反应速率慢。采用碱金属Na和过渡金属Ni对铁矿石载氧体进行修饰,在流化床反应器上研究了Na、Ni负载量和反应温度对煤化学链催化燃烧的影响。结果表明,在920℃时,Na-铁矿石的催化活性高于Ni-铁矿石,随着Na、Ni负载量的增加,煤化学链燃烧的反应速率加快,气体反应产物浓度达到峰值的时间缩短,反应后期气体产物的衰减速率变大,整个反应期间CO体积浓度明显减少,而CO2、H2体积浓度增大。当Na、Ni负载量均为6%时,两者进行比较分析,Ni在960℃时对煤化学链的催化燃烧效果最为显著,碳转化率高达92.7%,高于纯铁矿石约15.5%,而在800~920℃下,催化效果不明显;Na在800~960℃对煤气化反应的催化效果均较显著。SEM-EDX分析显示,反应结束后,Na-铁矿石载氧体表面Na盐流失严重,而Ni-铁矿石表面Ni盐负载较好。Abstract: The coal gasification rate is the limiting step during the chemical looping combustion (CLC) process. The effects of Na- and Ni-based additives loaded on the iron ore oxygen carriers on the chemical looping combustion (CLC) of coal were investigated in a fluidized bed. The influences of temperature, loading and cycle number on the performance of compound oxygen carriers were evaluated. The catalytic effect of Na is found to be higher than that of Ni at 920℃. The rate of reaction is enhanced with increasing the loading of Na and Ni. The peaks of all the exit gas concentration appear earlier and in the later stage the decay rate of that becomes larger. The concentration of CO in the exit gas is obviously decreased, whereas that of CO2 and H2 is increased. With a 6% loading of Ni, the catalytic effect of Ni on the carbon conversion is remarkable at 960℃, in which the carbon conversion is up to 92.7% that is about 15.5% higher than that using the iron ore. However, the effect of Ni on the carbon conversion is not obvious at 800~920℃. Compared with Ni, Na shows an obvious catalysis on the coal combustion of CLC in the whole experimental temperature region (800~960℃). The scanning electron microscope (SEM) and the energy-dispersive X-ray (EDX) analysis show that there is a severe loss of Na on the surface of used Na-based iron ore, but a less loss of Ni on the surface of used Ni-based iron ore.
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Key words:
- chemical-looping combustion /
- catalytic gasification /
- iron ore /
- natrium /
- nickel
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