Although the hydrogen reduction is thermally more disadvantageous than the CO reduction, it is advantageous that the reduction rate with H 2 is much larger than that with CO. In order to examine the effective use of hydrogen, the reduction of FeO 1.05 powder packed bed with H 2 -CO mixture was conducted, and the results were analyzed by a proposed model. The temperature, at which the reduction equilibria of FeO 1.05 with H 2 and CO equal, is determined to be 1 093 K from the present results. The apparent rate constants are determined to be 33, 8.6 and 15 for the reduction of FeO 1.05 with H 2 , CO and H 2 -CO mixture (V -H 2 : V -CO ϭ1 : 1), respectively. In the proposed model, when the water-gas shift reaction is taken into account, the additivity is established on the dependence of the rate constant of the reaction on the gas composition. When the water-gas shift reaction is not taken into account, the rate constant deviates negatively from the additivity. The apparent rate constants of the reduction determined in the present study take the middle values, and the contribution of the water-gas shift reaction is estimated to be 3 % against its equilibrium. In reducing FeO 1.05 with CO, the time when the sample is perfectly reduced is shortened by adding a small amount of H 2 , and the rate enhancement effect of H 2 on the gaseous reduction remarkably appears at 1 093 K. The effect originates in the proceeding of the water-gas shift reaction.

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It is necessary to reexamine basically an ironmaking process in order to reduce C02 emission and energy consumption in a blast furnace. Especially, direct reduction from wustite (FeO) to iron (Fe) stage of iron ore sinter with solid earbon in the blast furnace is a strong endothermic reaction. H, injection from the lower part of the shaft at temperatures from 1173 to 1373K can be considered more effective for the increase of the reduction degree from FeO to Fe. The effective conditions of H2 ratio in CO-C02-H2-N2 mixture and the reduction temperatures have been investigated in the bed packed with sinter by comparlng the reduction degrees from FeO to Fe between one method blown all the gases into the alumina ball bed (all gas mixed injection method or Method A) and the other method blown only H, through another nozzles into the lower end of the sinter bed without mixing (H2 non-mixed injection method or Method N).In the gas composition (C0+H2)/(C0+CO,+H,)=0.75 at 11 73 K determined by taking into account those in the blast furnace, the reduction rate was enhanced in the case of Method N. In the present work, the effective conditions of H2 ratio in CO-COrH2-N2 mixture and the reduction temperatures have been investigated in the bed packed with sinter (Fig, l) by comparing the reduction degrees from FeO to Fe between one method blown all the gases into the alumina ball bed (all gas mixed injection method ; Method A) and the other method blown only H2 through another nozzles into the lower end of the sinter bed without mixing (H , nonmixed injection method ; Method N).

The reactions for the deoxidation and the desulfurization of liquid iron by calcium are respectively expressed as follows:CaO(s)ϭCa(mass%, in Fe)ϩO(mass%, in Fe) .....(1) ISIJ International, Vol. 43 (2003) It is important to reduce the oxygen potential in steel in order to lower the sulfur content, and the addition of the strong deoxidizing agent, such as calcium, is considered to be most effective. The deoxidation and the desulfurization equilibria of liquid iron by calcium have been investigated at 1 873 K. The following thermodynamic values on the calcium desulfurization have been derived from the experimental results in the present study and in the previous studies by others.CaS (s)ϩCa (mass%, in Fe)ϩS (mass%, in Fe) log KϭϪ6.23 (Ϯ0.56) e S Ca ϭϪ22.4 (Ϯ6.4) , e S Ca ϭϪ28.0 (Ϯ8.0) (at 1 873 K) Using the thermodynamic data derived in the present study, the deoxidation and the desulfurization equilibria of liquid iron by calcium are proposed in the Fe-Ca-O-S system. The deoxidation and the desulfurization limits of liquid iron by calcium are calculated to be 1.6 mass ppm O (at 15 mass ppm Ca) and 3.5 mass ppm S (at 40 mass ppm Ca) under the condition of a CaO ϭa CaS ϭ1 at 1 873 K.