The liquid slag from the blast furnace is first solidified with water in the slag granulator. This generates a mixture of sand and water that will later be separated. Slag sand is one of the raw materials used in the cement industry. The water is pumped into the heat exhange system so that it can be used again in the cooling process.
Pig iron is one of the most important sources of iron used for crude steel production. Around 1.68 billion metric tons of pig iron are required worldwide each year - and this iron is primarily melted down in blast furnances. Blast furnance 2 in Duisburg-Schwelgern produces around four million metric tons.
Oxygen is required to gasify the coke and the pulverized coal. At least 70 percent of this oxygen comes from the air, which is compressed using blowers, and 30 percent is from pure oxygen, which is generated in air separation systems. This gas mixture is then heated to 1260 °C.
The interior of the 46-meter-tall furnace chamber is lined with fire-resistant brick. The diameter of the furnace opens to 15 meters in the tuyere area. The entire structure is surrounded by a steel framework.
This section contains four fans to supply the two blast furnaces in Schwelgern with cold air.
In the two cast houses, the pig iron and the slag are 'tapped' and separated. The pig iron that is extracted during the tapping process is transported to the 'torpedo ladles' and then sent off to the meltshop for further processing. The liquid slag is transported to the slag granulator.
Located in the cast house in the areas near the tapholes and the pig iron and slag spouts, there are hoods designed to extract and collect dust, which is then sent to a filtering system. A fine dust is created when materials are transported and sifted in the stock house. Here, the dust is extracted and filtered.
From here, the pulverized coal is pneumatically conveyed to the tuyere and then transported to the furnace using hot air. For each metric ton of pig iron, 150 to 200 kilograms of coal is injected as a substitute for the same quantity of the more expensive metallurgical coal.
If things are not working here, they are not working anywhere: The distribution station supplies blast furnace 2 with power.
The steel casing and fire-resistant brick of the blast furnace must be cooled. This is carried out through a number of closed-loop cooling circhuits. In the heat exchange system, the return water is cooled back down to the designated flow temperature.
The furnace conveyor transports the materials (lump ore, sinter, pellets, coke, and additional materials) from the stock house to the two charging containers at the head of the furnace.
The stock house contains day bins, weighing bins, and conveyor belts. The materials is stored here and then measured out by the weighing bins and delivered by the conveyor belts in the stock house. A computer ensures that the materials (coke, pellets, sinter, lump ore, or additional materials) are perfectly proportioned.
The reduction gases leave the process as furnace gases. These gases are purified and delivered to power plants or other consumers for use in energy production.
The materials fed into the furnace (iron ore, coke, additional materials) are pre-heated and dried from bottom to top by the hot, rising reduction gases.
The oxygen level of the iron oxide is reduced by chemical reactions at temperatures below 1,000 °C.
At temperatures above 1,000 °C, the carbon in the coke removes the rest of the oxygen from the iron oxide.
The hot reduction gas softens and melts the iron and the slag. Simultaneously, more carbon is released in the pig iron (carburization).
Before it reaches the tuyeres, the oxygen from the hot air reacts with the carbon of the coke and the pulverized carbon. At temperatures of around 2,200 °C, this produces the reduction gas carbon monoxide. This gas flows upwards against the coke and burden sliding in the opposite direction (countercurrent).
The slag and molten iron, which has a carbon content of around five percent, collects in the hearth, or the bottom section of the blast furnace, and both materials are released through the taphole at temperatures of around 1,500 °C.