ELECTRIC ARC FURNACE AC (PART 2) The Raw Materials (steel, steelmaking, furnace, iron, metallurgy)

1
ELECTRIC ARC
FURNACE AC (PT 2)
The Raw Materials

BEGINNER LEVEL
Author: Eng. Matteo Sporchia
Release date: August 27, 2019

Copyright – P4S – PRODUCTS 4 STEELMAKING
All Rights Reserved

2 Copyright – P4S – PRODUCTS 4 STEELMAKING – All Rights Reserved – Author: Eng. Matteo Sporchia
ELECTRIC ARC FURNACE AC (PT 2) – The Raw Materials

SUMMARY

1. INTRODUCTION ……………………………………………………..……………………….. PAG. 3

2. RAW MATERIAL TYPES ……………………………………………….…………..………. PAG. 4

3. RAW MATERIAL PROPERTIES …………………..………..………………………….. PAG. 17

4. ADVANTAGES / DISADVANTAGES OF THE RAW MATERIALS ………….. PAG. 18


1. INTRODUCTION

Through this report we are going to explain in details the most common raw
materials used in the Electric Arc Furnace (AC) based on the latest available
technologies. The charging of the raw materials is the primary step of the Electric
Steelmaking routes as shown here below:


The charging of the raw materials into the EAF has done through the
using of a proper bucket (or basket) that is a simple metal vessel that has an opening
mechanism on the bottom part. Normally more than one bucket has to be loaded to
allow the complete charging of the furnace. On the other hand some types of raw
material can be charged using an automatic continuous feeding system.

2. RAW MATERIAL TYPES
Raw material may be up to 100% scrap or various mixes of hot metal, pig iron, DRI
(hot and/or cold) and HBI.
Worldwide, scrap covers around 75% of the raw materials for EAF, while DRI and HBI
covers around 15% and the balance (10%) is covered by pig iron and hot metal.


2.1 SCRAP
Scrap is the mostly used raw materials for the EAF charge. It classification depends
on the grades of steel manufactured and the sorts of charge scrap available
commercially in the market. The following properties should be entailed for the sake
of the scrap material classifications:
• DENSITY Scrap density varies between light scrap (normally less than 0.5 t/m3) to
heavy scrap (up to 1 t/m3). The ideal avg. scrap density should be around 0.7
t/m3; Light scrap could be melted easily but require more number of buckets
while heavy scrap require more energy and can lead an increasing of refractory
and graphite electrodes consumption during the melting stage;


• GEOMETRY The knowledge of the scrap material geometry enables
optimum filling of the EAF charge baskets. The maximum size of the pieces
should be around 150 x 50 x 50 cm;
• QUALITY it depends from the presence of harmful / undesirable elements and
other factors such as the yield. Elements that can affect the quality of scrap
mainly include sulphur, phosphorus, copper e zinc;

Here below it shown a typical chemistry of the most common kind of scrap available
in the market:


2.2 DIRECT REDUCED IRON (DRI)
Direct Reduced Iron (DRI) is the product of the direct reduction of iron ore in the
solid state by carbon monoxide and hydrogen derived from natural gas or
coal. During direct reduction, oxygen is removed from iron ore reducing it to metallic
iron and the more stable oxide such as Silica (SiO2), Alumina (Al2O3), Lime (CaO),
Magnesia (MgO) and phosphorous (P).
Most gas-based direct reduction plants are part of integrated steel mini-mills, located
adjacent to the electric arc furnace (EAF) steel plant.
DRI can be either hot or cold charged to the EAF. Some steel companies ship DRI from
their captive direct reduction plants to their remote steel mills and a small volume of


DRI is sold to third parties. There are many small rotary kiln furnaces
producing DRI, known as sponge iron, using coal as energy and reductant source.
Some of the sponge iron plants are captive to steel mills.
The characteristics of DRI should be summarizes as below:
• CHEMICAL COMPOSITION The reduction process removes most of the oxygen
and sulfur from the iron ore, but leaves some impurities and gangue content.
Gangue consists of both acidic and basic elements. Basic elements include MgO
and CaO and acidic components include Si, Al and TiO2. DRI doesn't contain
tramp elements, just some traces of sulfur and phosphorus;
• CARBON CONTENT


• METALLIZATION Metallization is the ratio of Metallic Iron
compared to the Total Iron, including FeO). It could be from about 85% to around
95%, depending on the reduction process used. So metallization is a measure of
efficiency of direct reduction;


Different processes economically achieve different upper limits of
metallization. The table below represents some direct iron composition produced by
processes using different reductant and feed materials:


2.3 HOT BRIQUETTED IRON (HBI)
Hot Briquetted Iron (HBI) is a premium form of DRI that has been compacted at a
temperature greater than 650° C at time of compaction.
HBI is compact and the briquettes are easy to feed into the furnace. In contrast, scrap
is most unwieldy and sometimes needs cutting down, an expensive process.
Also for HBI we've to consider the parameters indicated for DRI such as chemical
composition, carbon and gangue contents and metallization.


2.4 PIG IRON
The average use of pig iron into EAF is about 5% of the total charging. Usually a
maximum of 15-20% of cold pig iron is used because it need a longer time to be melt
compared to the metal scrap. Pig iron is another group of materials in which the
chemical composition can vary quite considerable as shown in the table here below:


2.5 HOT METAL
Hot metal production is a standard part of operations in integrated steel mills. Hot
metal is produced in the blast furnace (BF) from iron ore pellets. This hot metal is
then refined into the basic oxygen furnace (BOF) in order to produce steel. Some
operations charge hot metal to the EAF by swinging the roof and pouring it into the
furnace. An alternative method of charging the hot metal is to pour it down a launder
which is inserted into the side of the EAF.


3. RAW MATERIAL PROPERTIES


4. ADVANTAGES / DISADVANTAGES OF THE RAW
MATERIALS
Many factors can determine the using of one or another raw materials. In general the
availability and cost of the raw materials (generally based on geographical area) will
determine the charge composition of the EAF.
Anyhow, we can summarize the advantages and disadvantages of the different raw
materials in the table here below:


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ELECTRIC ARC FURNACE AC (PART 2) The Raw Materials (steel, steelmaking, furnace, iron, metallurgy)

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ELECTRIC ARC FURNACE AC (PART 2) The Raw Materials (steel, steelmaking, furnace, iron, metallurgy)