Chemical-looping combustion (CLC) is a novel combustion technique with inherent CO2 separation.Magnetite (Fe3O4) was selected as the oxygen carrier.Shenhua coal (Inner Mongolia,China),straw coke and natural coke were used as fuels for this study.Influences of operation temperatures,coal to Fe3O4 mass ratios,and different kinds of fuels on the reduction characteristics of the oxygen carrier were investigated using an atmosphere thermogravimetric analyzer (TGA).Scanning electron microscopy (SEM) was used to analyse the characteristic of the solid residues.Experimental results shown that the reaction between the coal and the oxygen carrier become strong at a temperature of higher than 800℃.As the operation temperature rises,the reduction conversion rate increases.At the temperatures of 850oС,900℃,and 950℃,the reduction conversion rates were 37.1%,46.5%,and 54.1% respectively.However,SEM images show that at the temperature of higher than 950℃,the iron oxides become melted and sintered.The possible operation temperature should be kept around 900℃.When the mass ratios of coal to Fe3O4 were 5/95,10/90,15/85,and 20/80,the reduction conversion rates were 29.5%,40.8%,46.5%,and 46.6% respectively.With the increase of coal,the conversion rate goes up.But there exist an optimal ratio around 15/85.Comparisons based on different kinds of fuels show that the solid fuel with a higher volatile and a more developed pore structure is conducive to the reduction reactivity of the oxygen carrier.
