Effect of Temperature and CO₂ Concentration on Gasification Behavior of Carbon Fiber Containing Fine Iron Particles

摘要

In direct reduced iron (DRI) process, CO–H_(2) gas mixture is used as a reducing agent, which may make the operation unstable owing to a carbon deposition reaction and metal dusting reaction through Fe_(3)C. The Fe_(3)C decomposition reaction forms iron particles which acts as a catalyst for a carbon fiber deposition reaction at around 600°C. Such a carbon fiber deposition not only causes the loss of the carbon but also decrease the reducibility of the gas. On the other hand, the carbon fiber is likely gasified by CO–CO_(2) gas mixture at around 1000°C. In the present study, the carbon fiber gasification was quantitative analyzed using thermobalance to clarify the mechanism of the carbon fiber gasification reaction. To prepare a carbon fiber sample, the carbon was deposited with a reduced iron catalyst at 600°C in 50vol%CO-50vol%H_(2). Carbon fiber containing fine iron particles was gasified with various compositions of CO–CO_(2) gas mixture at 1000°C. Further, the effect of temperature of the gasified reaction was also investigated at 800°C, 900°C and 1000°C in 100vol%CO_(2). According to XRD analysis of the sample after gasification, Fe_(3)C in the sample before gasification decomposed to iron and a portion of iron was oxidized to Fe_(3)O_(4) and FeO when gasification ratio was high. The transition of carbon fiber shape was confirmed by SEM observation. Fine iron particles located on the tip of carbon fiber were sintered during gasification of carbon fiber. The mechanism of carbon fiber gasification was evaluated considering crystalline size, such as L_(a) and L_(c) that show (002) and (110) determined by XRD analysis, respectively. It was found that the L_(a) decreased with gasification ratio at all temperatures. In addition, L_(c) decreased after gasification at 1000°C.