Using Copper Ore and Hematite Fine Particles as Raw Materials of an Oxygen Carrier for Chemical Looping Combustion of Coal: Spray Drying Granulation and Performance Evaluation

Spray drying has gradually become an effective method for large-scale preparation of oxygen carriers as a result of its unique advantages (high efficiency, scalable production, etc.). However, expensive chemical or commercial powder is usually used as raw material in spray drying granulation. The main objective of this work is to reduce the cost of a spray-drying-derived oxygen carrier through using cheap natural ores as raw materials and optimizing the preparation process. Considering that hematite is cheap but less active in chemical looping combustion (CLC) processes, while copper ore has high oxygen carrying capacity and good reactivity but suffers from sintering at a high temperature, the bi-ore oxygen carrier is prepared by the spray drying granulation method in this work using copper ore and hematite fine powders as raw materials with the addition of a suitable dispersant and binder. Two kinds of oxygen carriers are successfully prepared by the spray drying method, Fe100 (the mass ratio of hematite is 100%) and Cu20Fe80 (the mass ratio of copper ore/hematite is 20:80%), and their performance is evaluated in a batch fluidized bed reactor. The reactivity of Cu20Fe80 is superior than that of Fe100 to char gasification products. The effects of the temperature, oxygen/fuel ratio, and coal rank on the coal-derived CLC performance of Cu20Fe80 are further examined. The temperature of 950 degrees C is the optimal choice with the highest reaction rate and CO2 yield. The gasification rate is fast using the low-rank coals as fuels, i.e., Chifeng lignite and Shenhua bituminous coal. Moreover, Cu20Fe80 exhibits good stability during the redox test of more than 10 cycles. The used oxygen carrier particles still maintain the abundant pore structure well without the sintering phenomenon. Additionally, the results of scanning electron microscopy with energy-dispersive spectrometry indicate that there is almost no decrease in the relative content of Cu elements after the cyclic tests. This work demonstrates that the spray-drying-derived Cu20Fe80 particle is a promising choice as an oxygen carrier for industrial application of the CLC process.