|Budget Amount *help
¥12,600,000 (Direct Cost : ¥12,600,000)
Fiscal Year 2000 : ¥3,600,000 (Direct Cost : ¥3,600,000)
Fiscal Year 1999 : ¥9,000,000 (Direct Cost : ¥9,000,000)
In pressurized conditions of 0.1-0.6MPa, 0.15-0.21mm particles of a hematite ore and a limonite ore were reduced in H_2-H_2S mixtures with α_s=Q.1-0.6 and carbupzed in CO-H_2-H_2S mixtures. In the study using the hematite ore,
(1) we have gravimetrically measured the carbide formation rate from reduced iron in the reaction gas of 0.1-0.6MPa at 500-700ーC, and formulated the rate for the carbide formation and determined the rare parameters.
(2) We have studied the carbide formation in a laboratory scale fluidized bed in the reaction gas of 0.1-0.6MPa at 873K by using the hematite ore, and
(3) we have tried to magnetically separate the iron carbide from gangue materials after the limonite ore blocks were reduced and carburized to cementite. We describe the results of the experiments blow.
(1) We have concluded that the carbide formation rate nearly obeys the integrated rate equation for the first order reaction -ln(1-f_θ)=g(p_bT)t as well as the rate at the atmospheric pressure does it. The c
arburization rate g(p_bT) obtained from the gradient in -ln(1-f_θ) versus t plot and the dependency of g(p_bT) on the composition, total pressure p_r and temperature T was investigated. As a result, we have found out that the value of g(pb_T) is piortional to the power of 1 at 600℃ and 1.4 to 1.5 at 700℃ to Pr. Based on the dependence, we have concluded that the rate controlling step is the dissociative adsorption step of CO at 600℃ but it gradually shifts to the mixed control of the dissociative adsorption step and the adsorbed oxygen removing step by CO and H_2. From the elementary reaction mechanism, an overall rate equation was derived for the carbide formation and the rate parameters were determined, from which the calculation of the carbide formation rate was enabled with the fluidjzed bed. The influence of reduction and carburization temperature on the carbide formation was also investigated.
(2) We have measured the carbide formation rate from reduced iron in a fluidized bed with the reaction gas under the pressurized condition. Carbide formation curves were established from the composition of samples, which were taken every 600-900s interval and determined by XRD and carbon analysis. Also for the bed, the curves nearly obeyed the integrated first order reaction rate equation and the value of g(p_bT) was obtained as the gradients in -ln(1-f_θ) versus t plot. And we found that the g(p_bT) is proportional to the 1 power to p_r at 600℃. Furthermore, by analyzing the composition of the outlet gas from the fluidized bed, we have determined the relative contribution to the total removal of the adsorbed oxygen ; by O(ad)+H_2→H_2O and O(ad)+CO→CO_2. As a result, the oxygen removal for carbide formation is mainly based on the former reaction and the oxygen removal for free carbon is mainly based on the latter reaction. Furthermore, we proved that pressurizing enhances the carbide formation rate. We have proposed two reaction models, I.e. plug flow reaction model and bubble assemblage model and indicated the applicability of the models to the carbide formation curves. These models can contribute thescale up of the carbide formation in fluidized bed.
(3) We produced iron carbide by reducing a limonite ore block and carburizing the reduced iron. After pulverization, we tried to separate the iron carbide from gangue materials by magnetic separation method. As a result, we have found out that we can hardly separate the gangue materials, which contains at most 8 mass% gangue materials, from iron carbide even by using magnetic separation method. Less