Investigation of the water vapor influence on the performance of iron-, copper-, and nickel-based oxygen carriers for chemical looping combustion

The water vapor (WV) influence on the reactivity and capacity of three commonly used oxygen carriers (OCs), iron, nickel, and copper based on chemical looping combustion, was investigated. OC samples with increasing metal loadings on the alumina support were prepared through freeze granulation (FG) and evaluated by a thermogravimetric analyzer-mass spectrometer coupled water vapor generator system (WVG-TG-MS) under cycling reducing-oxidizing gases at 950 C. The comparative study in dry and wet simulated syngas showed that the reactivity and oxygen carrying capacity was reduced to varying extents for the three types of carriers by the addition of 10% WV. Under dry conditions, the copper- and nickel-based carriers showed higher reactivity and larger capacity in the reduction and oxidation cycles than iron-based carriers. However, the iron-based carriers presented better resistance to the WV influence than the other two. Under the wet condition, the performance difference among the three types of OCs became less significant. Metal loadings were also found to affect the resistance of carriers to the presence of WV. A series of direct coal combustion experiments was performed in the TGA-MS system as well to study the effect of WV in solid-fueled combustion. The rate of weight loss of the OC/char mixture in Ar with 10% WV at 950 C was approximately 4 times faster than that in dry Ar, suggesting that the presence of WV promoted in situ char gasification and increased the overall reaction rate and completeness of the solid fuel combustion.