Catalytic combustion of coal using alkali and transition metals loaded on iron ore oxygen carrier

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.