Abstract
Since the war we have operated the blast furnace by charging only domestic iron ores and produced pig iron with the average content of sulphur running up to 0·17% in 1946. Before charging the domestic ores the average content of sulphur in the charged raw material was about 12 to 14kg. per ton of pig iron tapped, but recently it has increased up to 25 to 30kg. Generally 70 to 75% of the sulphur runs out with the slag and 20 to 25% of it with the gas. The average content of sulphur in the coaking coal was 0·7% and practically none of the sulphur decreased by washing nor coking. The content of sulphur were generally large in the fine and sintered ore under 10 mm sizes.
Generally the ratio of desulphurization by sintering is from 80 to 90% and it is possible to make it over 90% by improving the method of crushing and screening.
To desulphurize by briquetting it is necessary to roast it up to 1200°C. By using the cement rotary kiln we found out that it is possible to desulphur the lump ore from 70 to 80%. Desulphurization within the blast furnace is 94 to 95% which gives the same ratio and shows no difference whether it be foreign or domestic. Decrease in the blast pressure and the furnace tempeture give a bad effect on desulphurization. It is desireable to have a content of 1·0 to 1·5% of Mn in the pig iron and a basicity over 1·3 in the slag. After tapping about 25 to 35% are desulphurized in the ladle on the way to the pig casting machine and about 30 to 35% when the molten pig are traosfered to the open hearth plant by way of dead mixer. It is also possible to desulphurize 40 to 60% by adding 3 to 5kg. of soda ash per ton of pig iron, but at present soda ash are not available. About 15% of the sulphur are removed by slagging off in the dead mixer.
We have come to the conclusion that in order to reduce and refine domestic iron ores it is best to screen it into lump and fine ores and then give the desulphurizing treatment accordingly. This is not impossible but it requires tremendous effort and time.
