Steelmaking Methods
One of the most important industrial processes is steel manufacturing. It has followed civilization’s technological development because of its characteristics of high strength and ductility. In fact, 3 different ways of steel production are:
- The Blast Furnace (BF)
- The Direct Reduction (DR)
- The Electric Arc Furnace (EAF)
The Blast Furnace (BF) plants were built for the production of large amounts of steel. The beginning of a melting metallurgical process is composed of the reduction of iron ore. In the BF, Cast Iron is produced and after that, by blowing oxygen in the converter, it is turned into the steel.
The Direct Reduced Iron (DRI) is usually used in its briquette form (Hot Briquetted Iron (HBI)) for easier transportation and it can be charged in the blast furnace (BF), inside the converters (BOF) and in the Electric Arc Furnace (EAF).
The cycle of EAF is based on the metal scrap melting. The HBI manufacturing process involves the usage of a reformer with the conversion of natural gas to hydrogen (H) and CO (the reducing gas) in a vertical furnace. This furnace creates the reduction reactor and a heat recovery unit. Energy-wise, the production process is cheaper if compare to the cast iron production, since it is not essential to make the iron ores reaches the melting temperature, contrary to the blast furnace (BF). In addition, establishment costs are considerably less than the full cycle of steel manufacturing.
Sustainable steel-making goals
the final goal of modern society is reducing the environmental effects, especially for the iron and steel-making industries. According to one of the researches[1], the sustainable steel-making goals are:
- preservation of natural resources,
- reduction of greenhouse gas emanation,
- reduction of volatile emanation,
- reduction of landfill waste,
- reduction of dangerous waste.
BF/BOF vs EAF
Comparing the properties of iron and steelmaking technologies:
- BF/BOF has consumption of equipment and emissions 2-4 times higher and this requires more energy & water consumption. Moreover, it needs higher energy for the production due to the coke making and sintering processes.
- EAF has somehow larger emissions of greenhouse gas of produced metal, compared to DRI, mostly due to the use of electricity, at the same time in the DRI process, only natural gas is applied to reduce the iron ore. Emission of SO2, CO is not meaningful in DRI technology.
[su_note note_color=”#f8f8bc”]The use of the DRI as a substitution of cast iron, in order to increase the cold charge in BOF, is an innovative nature.[/su_note]
HBI Advantages
The HBI’s advantages are:
- high electrical and thermal conductivity;
- high bulk density, which causes saving space;
- minimum reactivity with salt & freshwater.
- chemical properties are well-known & verified by the producers;
- the lowest value of harmful elements, such as Cr, Sn, Cu, Ni, Mo, V, and Pb;
Use of DRI and HBI in a blast furnace (BF)
DRI and HBI are used in BF for producing pig iron. Right before the melting time, the BF is involved by the presence of DRI and so, the charging of DRI and HBI targets to evade the reduction processes required to reduce only a fraction of the charged raw material.
Use Of DRI and HBI In Basic Oxygen Furnace (BOF)
The BOF steelmaking process consists of 3 main steps:
- converter charge;
- blowing of the oxygen;
- using the ladle.
A bright further of the coke consumption reduction and the blast furnace productivity increase can be achieved by the introduction of DRI and HBI enriched by carbon.
Use Of DRI and HBI In Electric Arc Furnace (EAF)
The physical composition of DRI and HBI and their perfect allocation inside the EAF buckets influence the quality and the metallurgical yield.
DRI and HBI melt very fast because of the great conductive heat transfer, thus it must be charged in the second bucket. A suitable charging of DRI and HBI will help the stability of the arc as well as the protection of the furnace lining.
When DRI is charged, the key factors affecting the consumption of electricity are:
- Quality of DRI AND HBI, including contents of Fe M (metallic iron), C (carbon), SiO2/Al2O3 (gangue), S (Sulfur), and P (Phosphorus);
- The temperature of DRI AND HBI;
Conclusions
DRI and HBI usage in a blast furnace (BF) allows the reduction in charged coke, the emission of CO2 and the concentration of sulfur in the tapped cast iron;
in the BOF and in the EAF, a properly-carburized metal bath, such as pig iron, lets the recovery of the FeO in the DRI and HBI on;
in EAF way, DRI and HBI don’t have to be charged by the first bucket since this kind of raw material needs to be added to a molten bath enriched by carbon.
[1] New steelmaking processes: drivers, requirements and potential impact. Fruehan. s.l. : Ironmaking Steelmaking,2005, Vol. 32.
Source: https://www.researchgate.net/publication/304878005_Use_of_DRIHBI_in_ironmaking_and_steelmaking_furnaces
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