This paper concerns the degree of indirect reduction in a burden rising substantially in an oxygen blast furnace. It studies the pellet, sinter and a mixture of both in different cases. The paper concerns experiments on single particle load softening to investigate the microstructural evolution of different burdens during the softening and melting process. The results of the experiments show that the degree of reduction impacted the softening and melting behaviour. In the case of a low degree of reduction, a slag phase substrate and a myrmekitic iron structure were formed on the periphery area of the molten burden, whereas slag phase substrate and disperse island wu ¨stite structure were formed in the centre area. Both peripheral and central areas had a slag phase substrate and myrmekitic iron texture. The slag-iron distribution had a structure in which the slag phase was cut in the metal iron phase. The content of 2FeO.SiO 2 as a low melting point phase in the slag decreased sharply, and this resulted in the increase in slag-iron separation temperature. The variation of the Ca/Si ratio in the interface between the pellet and the sinter indicated that enhancement of the reduction degree caused the initial temperature of the interaction in the mixed burden to rise and the interaction distance to decrease.

The reduction behaviour of sinter and pellets was investigated by a programmable reduction apparatus to simulate the traditional blast furnace (TBF) and the oxygen blast furnace (OBF). The starting temperature for reduction of sinter and pellet in the OBF decreased 60 and 150uC compared with that in the TBF and, by the time the temperature reached 1100uC the reduction degree of sinter and pellet was 100.0 and 98.7% in the OBF compared to 94.0 and 83.1% in the TBF. The trends of the reduction rate of sinter and pellet were consistent in OBF and TBF. There are two peak values at about 60 and 80 min and in the OBF the third peak value of pellet emerged at 40 min. In addition, the mineral microstructures of the ferrous burden were characterised by means of SEM and the area proportion of metallic iron zone was obtained by SEM photos.

The OBF process is widely studied as an alternative ironmaking process, due to the social pressure of energy and environment at present. A comprehensive mathematical model of the OBF process is established, which is based on material and exergy balances. The process parameters of the OBF with different oxygen enriched blast were calculated through the model. The calculation results demonstrated that the material balance of carbon input in the OBF process decreased by 6.7% (OBF-I) and 22.4% (OBF-II) compared to the TBF process. Also, the industrial oxygen consumption increased from 185.88 m 3 (OBF-I) to 228.32 m 3 (OBF-II). The exergy output and the total exergy loss of the OBF-I process decreased by 1.5% and 5.6%, respectively, and those in the OBF-II process decreased by 16.60% and 30.81%. Due to the exergy indices in OBF-II process all improved, the OBF-II process was a significantly efficient ironmaking process compared to the TBF.