Investigation on high-temperature reactions of organic compounds and its control for efficient utilization of complex wastes in the ironmaking process

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In the ironmaking process, increasing in the production rate and lowering the reduction temperature of iron burdens are urgent issues to save energy consumption and therefore to minimize CO_2 emissions. The reduction of iron ore composite containing carbonaceous materials has been developed as one of the promising processes to cope with such problems. On the other hand, waste plastics have potentials to supply the reducing gases such as H_2, CO and CH_4 through their pyrolysis process. Utilization of such gases for the iron ore reduction process is one of effective ways to reduce the CO_2 emissions.The objectives are to understand the reduction behavior of the hematite composite with reductants particles and to clarify its optimum structure. polyethylene and graphite were used for the reductants. The former was as a model material of organic wastes. The composite was heated up to 1427K with the heating rate of 0.6-3.7K/s. The contribution of polyethylene to the reduction of iron oxide was determined by carrying out the continuous analyses of the generated gas concentrations and the microstructure observation.The contribution of polyethylene was limited when the hematite composite uniformly-mixed with the reductant was used. The addition of excess polyethylene to the composite hardly acted as reductant. The addition of graphite to the hematite composite containing polyethylene led to higher reduction degree. This is because the formation of cracks inside the composite enhanced the direct exhaust of generated gas without the contribution to the reduction reaction. On the other hand, the double-layer composite, whose polyethylene content in the center layer was larger than that in the inner, showed an effective utilization of polyethylene compared to the homogeneous composite. The composite material with the double-layer structure can be applicable to the ironmaking processes using rotary hearth furnace and moving bed.