Unit 5
Production of pig iron
Iron ore and scrap – mines, recycling
Steel is produced from iron ore and scrap. Iron ore is a mineral
aggregate that can be converted economically into iron. The quality of
the iron ore is mainly determined by its composition: high iron content
and low sulphur and phosphorus contents are favorable. Iron ore can be
found all over the world, but its iron content varies.
Steel scrap has been effectively collected for several decades and is recycled as a valuable raw material for steel production.
There are two main processes for producing steel: by means of a blast
furnace (indirect reduction) in combination with a converter, or by
means of an electric furnace. In the former process, iron ore is the
main raw material. In an electric furnace, scrap iron is used and
occasionally also sponge iron. Sponge iron is an intermediate product,
which is produced from iron ore by means of direct reduction (DRI or
directly reduced iron) and then further reduced and smelted in an
electric furnace.
Exercise 1:
Please select technical terms from the text below and translate them:
Primary and secondary steel making
Integrated steel works include a blast furnace and a converter to
produce liquid steel. This is also called blast furnace steel making or
primary steel making. In addition to iron ore, about 20% scrap iron is
also used in this process. The energy required to melt this iron is
provided by fossil fuels. Before the raw materials (iron ore and coal)
are suitable for use in the blast furnace, they have to undergo
intensive preparation.
Electric furnaces on the other hand are charged with 100% scrap iron or
with iron ore or direct reduced iron (DRI). These materials melt by
putting in large amounts of electrical energy by means of an electric
arc. Hence their name: Electric Arc Furnace (EAF) also called secondary
steel making. Steel production in electric furnaces no longer requires
intensive preparation of raw material. Because the charges of an
electric furnace are smaller, they can meet the demand more flexibly.
But the process also has its limitations: quality and price of scrap
metal are of overriding importance. Besides, some elements present in
the scrap metal are retained in the liquid steel.
Answer Key: Exercise 1
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Exercise 2:
Iron ore -
Scrap -
Mineral aggregate -
Indirect reduction -
Sponge iron -
Before being used in the blast furnace, iron ore, coke, fluxes and air are pre-treated to ensure that the blast furnace process proceeds optimally.
Coke is produced from coal. Coal is not suitable for direct use in a blast furnace since it contains too many harmful or useless constituents for the reductive smelting process. Moreover, coal is not strong enough to bear the blast furnace charge. The conversion from coal to coke takes place in the coking plant, in the coke ovens at a temperature of up to 1100 ˚C. Since no oxygen is present in these ovens, the coal does not burn. This process is called dry distillation. It liberates a large quantity of gas and smoke, which, after purification, yields coke oven gas and other valuable commodities such as tar, ammonia and benzene. When the coal has been converted into coke, the coke is removed from the oven and quenched by spraying with water. Then the coke is crushed and screened until its granule size is suitable for use in the blast furnace. To reduce coke usage in the blast furnace, pulverized coal is also used. This pulverized coal is injected via tuyeres into the smelting section.
The production capacity of the blast furnace is increased by first converting fine iron ore and additives into sinter rather than charging the ore as such directly to the blast furnace. Sintering is the agglomeration by heat of fine ores, fluxes and recuperated materials. The mixture is heated briefly in the sintering plant up to about 1400 ˚C. This makes the components agglomerate. The cake is then crushed and screened, after which it is ready to be charged into the blast furnace.
Exercise 3:
Exercise 4:
Translate the following text into Czech:
Coke is produced from coal. Coal is not suitable for direct use in a
blast furnace since it contains too many harmful or useless constituents
for the reductive smelting process. Moreover, coal is not strong enough
to bear the blast furnace charge. The conversion from coal to coke
takes place in the coking plant, in the coke ovens at a temperature of
up to 1100 ˚C. Since no oxygen is present in these ovens, the coal does
not burn. This process is called dry distillation. It liberates a large
quantity of gas and smoke, which, after purification, yields coke oven
gas and other valuable commodities such as tar, ammonia and benzene.
When the coal has been converted into coke, the coke is removed from the
oven and quenched by spraying with water. Then the coke is crushed and
screened until its granule size is suitable for use in the blast
furnace. To reduce coke usage in the blast furnace, pulverized coal is
also used. This pulverized coal is injected via tuyeres into the
smelting section.
Answer Key: Exercise 4
Blowing large amounts of air into the blast furnace maintains the process. The air is taken from outside and blown by ventilators to the hot blast stoves. There the air, also referred to as blast, is preheated to about 1200 ˚C. The main reason for pre-heating the air is to reduce coke consumption: the heat supplied by the hot air no longer has to be supplied by burning the fuel (coke). The pre-heated air is fed to the lower part of the blast furnace vie tuyeres that ensure an optimal air distribution inside the blast furnace.
Exercise 5:
Use Internet for the following task:
Why is a blast furnace called a blast furnace and not a “tall” furnace comparing to Czech “Vysoká pec“ or German “Hochofen”?
Answer Key: Exercise 5
The carbon monoxide gas is formed in the lower part of the blast furnace and rises up inside the blast furnace. At the same time, the descending charge comes into contact with this reducing gas, as a result of which liquid pig iron is formed and collects in the bottom of the blast furnace. The pig iron is tapped from the blast furnace at regular intervals. Just above the tuyeres, the oxides that have not been reduced react with each other to form slag.
Exercise 6:
During the production of pig iron, a substantial amount of gas is formed within the blast furnace. The gas is collected at the top of the blast furnace and purified. It can be then supplied to a power plant where it serves as fuel for electricity generation.
Exercise 7:
Translate the following text into Czech:
The formation of a slag that flows properly through the furnace charge is vital for the removal of all unwanted elements from the pig iron. The slag consists of complex compounds of calcium, silicon and magnesium. The slag is tapped from the blast furnace together with the liquid pig iron. A skimmer separates the slag from the pig iron in the slag runner.
Answer Key: Exercise 7
Exercise 3:
Exercise 6:
Points to remember:
- Products that are used in the blast furnace:
Top: In through the charging system – Sinter, Coke, Additives
Bottom: In through the tuyeres – Hot air, Pulverized coal
- Products that are formed in the blast furnace:
Top: Out through the gas exhaust – Gas
Bottom: Out through the tap hole – Pig iron, Slag
| English | Czech |
| Agglomerate | Aglomerát, spečenec |
| Blast furnace | Vysoká pec |
| Coke | Koks |
| Directly reduced iron (DRI) | Železo po přímé redukci |
| Flux | Tavidlo |
| Sintering | Spékání, aglomerace |
| Skimmer | Odlučovač strusky |
| Slag | Struska |
| Slag heap | Halda |
| Slag runner | Struskový žlab |
| Sponge iron | Houbovité železo |
| Tuyere | Výfučna |
Gallery:
Flow Chart
|
Coke
|
Sinter
|
Slag
|
Sinter Plant
|
Blast Furnace
|
Blast Furnace
|
Blast Furnace
|
Sources:
Meseure, K., Steel Making, ArcelorMittal R&D Gent, ArcelorMittal University - Understanding Steel, 2009
Velzeboer, M., Mining, ArcelorMittal University - Understanding Steel, 2009
PC Translator. CD-ROM. Korytná:LangSoft & SOFTEX Software, 2007
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