Evaluating the behavior of catalyst coated nut-coke in blast furnace conditions

For efficient blast furnace ironmaking, it is desired to have low reducing agent rate, primarily coke rate. Developing technology to improve reaction efficiency of the blast furnace is extremely important as it has the potential to allow a decrease in the reducing agent rate as well as CO2 emissions. The reaction efficiency of blast furnace can be improved by lowering the Thermal Reserve Zone (TRZ) temperature; which is also the starting temperature of coke gasification reaction. In present study, nut-coke has been coated with in-plant waste, consisting mainly of iron oxide and calcium oxide, as catalyst. There was a clear increase of 10 points in the reactivity of coated nut-coke. The coated nut-coke have been subjected to non-standard high temperature experiments simulating blast furnace conditions with reducing gas consisting of CO, CO2 and N2 to capture the effect of catalytic coating on the onset of gasification reaction. The high temperature experiments carried out advise the following: i) A drop of 100 °C in the reaction beginning temperature of catalyst coated nut-coke as compared to non-coated one ii) A typical calculation shows that the lowering of reaction beginning temperature corresponds to a potential carbon rate savings of about 2.5 kg/ton of hot metal (thm). Furthermore, in a trial conducted at blast furnace with charging catalyst coated nut-coke, it has been observed that the carbon rate during the trial period was 3 kg/thm lower than the base period. The findings of blast furnace trial agree with that of the experimental one.

Attempts to replace nut coke with semi-coke for blast furnace ironmaking

Low coke rate for blast furnace operation has been required in response to the rising cost of coking coals. To extend the utilisation of coal resources, semi-coke has been introduced to blast furnace ironmaking process in recent years, however, there are still many issues unclear about the effect of semi-coke on ironmaking process. In this study, the possibilities of using semi-coke as alternative fuel for nut coke were studied. The characteristics of semi-coke including mechanical strength, high-temperature strength/reactivity, carbon gasification as well as direct reduction were studied and compared with small size metallurgical cokes (nut cokes). The results showed that semi-coke has higher CRI values, especially at higher temperatures and in a mix-charging pattern. Semi-coke was found to have a higher gasification reaction rate and depleted at lower temperatures. The reduction results showed that with participating of semi-coke the reaction starts at lower temperatures. In addition, the study suggested that semi-coke exhibits the advantages of low ash and sulphur contents, although it has lower mechanical strength, it would protect the lump coke by shifting the carbon gasification to itself, therefore, mixing semi-coke would benefit the blast furnace operation and lower the coke rate.