Tateo Usui

Abstract:

The exhaustion of natural resources (quantity and quality) and the CO2 emission control is becoming a more and more important subject to get over in steel industry. Effective uses of coal and woody biomass, especially their carbonization gas, were discussed in pre-reduction of iron oxide pellets for total smelting reduction process using coal or carbon composite iron oxide pellets using semi-char and semi-charcoal to investigate the possibility to overcome these subjects. The factors influencing upon reduction rate of carbon composite iron oxide pellets we studied were the effects of the maximum carbonization temperature Tc,max to obtain the semi-char or semi-charcoal, sorts of coal and wood, particle size of the carbonaceous material, constant ambient temperature or heating rate to reduce the composite pellet, and addition of hydrogen in an atmosphere. The samples used were Newlands coal, Newcastle blend coal, Muswellbrook coal, Japanese cedar and Japanese cypress. The data analyses of the carbonization gases from coal and woody biomass have also been carried out to evaluate their chemical and thermal possibility. As Tc,max decreases, the emitted carbonization gas volume decreases and the residual volatile matter increases. The heat value of the carbonization gas depends on Tc,max and consequently on the emitted gas volume and the composition. As a whole, the total heat value tends to increase almost monotonically, as Tc,max increases. The rate enhancement effect of reduction for semi-charcoal composite pellets is stronger than that for semi-char composite pellets, because the gasification rate of semi-charcoal is higher than that of semi-char. This is because the amorphous nature of semi-charcoal is stronger than that of semi-char and the activation energy of semi-charcoal is lower than that of semi-char. The reduction rates for both semi-char and semi-charcoal composite pellets increase as Tc,max decreases. By decreasing Tc,max, the activation energy Ea of semi-charcoal decreases, or the reactivity 1/Ea increases. An optimum point of Tc,max may be obtained to meet the best choices both for the reactivity and the total carbonization gas volume or the heat value.