Blast Furnace System in steelmaking process
By:Yvonne Aug 10, 2020
Blast Furnace System:
In a blast furnace (BF) the iron oxides are reduced and the resulting iron is melted. Approximately 70% of the global steel production involves the use of BFs. Sizes of BFs installed cover a very wide spectrum, ranging from less than 100 m3 to more than 5000 m3. Larger BFs have less heat losses and enable installation of heat recovery equipment more cost effectively.
Cold blast blowers, and hot blast ovens are other important elements of the BF system. While the former provides the necessary air flow at 3 – 5 bar pressure, the latter increases the temperature of air to 900 – 1350 oC. Ore, sinter or pellets, coke and lime (that removes impurities and acts as flux) are added to the blast furnace from the top, whereas hot blast (compressed air) is introduced from tuyères at the lower part. Auxiliary reductants/fuels – like coal, fuel oil, natural gas, or other alternative sources – can also be injected from the bottom of the furnace. At lower parts of the furnace coke is gasified and the resulting CO reduces ironoxides as it ascends in the furnace. The molten iron trickles down and collects at the bottom. The impurities that are removed by the aid of CaO form a slag that floats on the molten iron. The hot gases leaving the blast furnace still maintain a pressure of 2 – 3 bar. In addition, a gas with low calorific value (~ 3 MJ/Nm3) is produced at a rate of 1300 – 2200 Nm3/t-pig iron. After cleaning, this gas can be used as fuel.