What is direct reduction iron process

Scheme of a blast furnace and process steps

Cast iron and steel are made from pig iron. This pig iron is produced in the blast furnace, as long as it is not in small quantities as it is used in jewelry production.

The furnace


Below are two pictures of a modern blast furnace:

The next picture shows the process of tapping the melt:

The structure of a common blast furnace is shown in the following graphic:

Information on the individual components:

  • Furnace stage: In addition to the furnace gas pipes and the inclined elevator, it is supported by a special frame.
  • Top hatch: Represents a sluice with which charging is made possible without a change in the firing atmosphere [gas content, temperature, pressure] occurring.
  • Gout: coat made of gray cast iron or steel.
  • Shaft: steel jacket lined with refractory stones. It also has a cooling system made up of water pipes.
  • Rast: Also contains water pipes for cooling.
  • Frame: Cooling takes place by sprinkling water on the sheet metal armor.
  • Ring line: Distributes the hot air and is also refractory bricked.
  • Nozzle block: Equipped with fireclay, it guides the hot wind from the ring line to the blow molds, up to 38 pieces.
  • Blow molding: Double-walled pipes that are water-cooled and extend 0.1-0.3 m into the furnace chamber.
  • Slag shape: double-walled pipes with water cooling that allow continuous removal of slag [slag]
  • Tap hole: closed with refractory mass. This stopper is either driven into the oven or burned open with an oxygen lance.

Technical specifications:

Interior of a blast furnace


Masonry: the inside of the entire furnace is lined with fireclay bricks, only the lower part is provided with carbon bricks.

Height: Some blast furnaces are up to 100 m high, including the supporting frame.

Diameter: 3-7 m [gout], 6-16 m [coal sack], 3-14 m [frame]

Wall thickness: 0.7-0.9 m [shaft], 0.6-0.8 m [detent], 0.8-1.5 m [frame]

Blast furnace process

The blast furnace process is the most common method for producing pig iron, as it enables not only high efficiency but also good automation. In addition to ore, the input materials are primarily coke and aggregates.

The task of the coke is to act as a reducing agent for the ore and a carbonizing agent for the pig iron. The aggregates, on the other hand, remove unwanted by-products of the ore - the gangue - by building up chemical compounds and then transferring them to the slag.
The blast furnace itself uses the countercurrent process. While the feedstock is being conveyed from top to bottom, the gas flows in the opposite direction. The chemical reactions take place in parallel to these currents. These are:

  • Burning the coke,
  • Implementation of the gas,
  • Reduction of iron ores,
  • Slagging,
  • Side reactions.

At the beginning of the process, the ore is still in the following forms:

  • Magnetite $ \ Fe_3 O_4 $
  • Minette $ \ Fe_x (OH) _y $
  • Hematite $ \ Fe_2 O_3 $

For an optimal result, the ores are broken down to a small size and the aggregates are added. This combination is also called Möller, which is fed to the blast furnace layer by layer together with the coke. The layers then move from top to bottom.

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At the Möller it is a mixture of iron ore and aggregates such as lime. With the help of these additives, the slag, in which the impurities are bound, is formed.

The process reactions are as follows:

  • 1. Drying, preheating, expulsion of the water hydrate
  • 2. Indirect reduction
  • 3. Direct reduction
  • 4. Melting process
The Boudouard equilibrium between $ C, CO $ and $ CO_2 $ is decisive for the processes in the blast furnace

$ \ rightarrow: CO_2 + C \ leftrightarrow 2 CO $

It describes the process in which the $ CO_2 $ formed during the reduction of iron oxide by $ CO $ is converted back to $ CO $ by a reaction with C and this can then be used for a further reduction. The temperatures required for this are above 1000 ° C.