The melting characteristics of Vietnamese ilmenite and manganese ores used in chemical looping combustion

For chemical looping combustion (CLC) of solid fuel such as coal, char gasification kinetics is relatively slow and is the rate controlling step, so a high temperature is needed in order to enhance char conversion. However, the maximum allowable temperature in CLC depends on the property of oxygen carrier, and the melting state of the oxygen carrier is the upper limited temperature of the CLC reactors. Therefore, it is necessary to investigate the melting behaviors of oxygen carriers. In this work, a melting test setup with an optical camera-image system was used to experimentally study the melting characteristics of one vietnamese ilmenite and 7 kinds of manganese ores at inert and reducing condition. In inert atmosphere, the prototype temperature and flowing temperature are 1402 degrees C and 1500 degrees C for the oxidized ilmenite respectively, while reducing atmosphere can significantly decrease the melting temperatures of the oxygen carrier particles, the prototype temperature and flowing temperature of ilmenite in reducing atmosphere are decreased to 1337 degrees C and 1403 degrees C, respectively. An important finding is that the melting temperatures of oxidized manganese ores are significantly lower than that of the oxidized ilmenite. Different manganese ores have different melting temperatures, and for some manganese ores, the prototype temperature can decrease to less than 1000 degrees C. It was also found that the melting behaviors between the ilmenite and manganese ores have large differences. When heated up to the deformation temperature, the ilmenite melted rapidly within 8 degrees C-29 degrees C, whereas manganese ores melting had a wide temperature range from 38 degrees C-301 degrees C. It can be concluded that the maximum operational temperature of CLC reactors should be less than the prototype temperature of oxygen carrier particles in the actual environment. The operational temperature of CLC reactors when using ilmenite can be higher than that of using manganese ores as oxygen carriers. However, for manganese ores, it could be dangerous for fuel reactor when the operational temperature is higher than 950 degrees C.