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Eng.Shoukery
Meltshop
Process
EAFEAF
SteelmakingSteelmaking
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Ironmaking
Blast furnace (pig iron)
Direct Reduction Process (DRI)
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MagnetiteHematite
LimoniteGoethite
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Iron Ore
Major producers of iron ore include Australia, Brazil, China,Russia, and India
The principle ores of iron are Hematite, (70% iron) andMagnetite, (72 % iron). Taconite is a low-grade iron ore,containing up to 30% Magnetite and Hematite
There are 800 billion tons of iron ore resources, containingmore than 230 billion tons of iron. The U.S has 110 billiontons of iron ore representing 27 billion tons of iron.Worldwide, 50 countries produce iron ore, but 96% of thisore is produced by only 15 of those countries
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Blast Furnace Reactions
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Pig Iron Chemical
Composition
Pig Iron Chemical Composition :
C: 3.5-4.5%; Mn : 0.4-1.0%; Si: 0.5-1.2%;P: 0.15% Max; S: 0.04% Max
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Scrap Price
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Pig Iron Chemical Composition : C: 3.5-4.5%; Mn : 0.4-1.0%; Si: 0.5-
1.2%; P: 0.15% Max; S: 0.04% Max
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DRI Production Process
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Fe2O3 +CO = 3CO2 +2Fe
Fe2O3 +3H2=3H2O+2Fe
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Chemical Characteristics- The direct reduction process removes most of the oxygen and sulfur
from the iron ore, but leaves all of the impurities and gangue content
-Metallization (the ratio of metallic iron to total iron, including FeO)depends on the type of process used to produce DRI and ranging from
85-95%- DRI contains no tramp elements (scrap contains elements such as Cu,
Zn, Pb, Sn, As, Cr, Ni, and Mo); it only contains traces of sulfur and
phosphorous.
Physical Characteristics- The best diameter of DRI pellets for furnace charging is 6-16mm
(diameters less than 3mm are called DRI fines, and not pellets).
- Apparent density: 2-3ton/m3
- Bulk density (accounts for air gaps): 1.6-1.9 ton/m3
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DRI/HBI Storage DRI is reactive to free water and oxygen, therefore DRI must be
cooled before shipping
DRI Can be subject to a high degree of reoxidation. Self ignition canoccur if a natural air draft through the pile. the pellets buried insideare wet and volume of pile insulate heat loss
Fires result when DRI pellets are placed on top of wet material. To
stop the fire the pile must be spread to height of one-half meter or pile bury under sand or slag. Storage silo fire deal by flooded withextremely large amount of water but the area must be evacuated dueto h2 evolving.
At .6 m below surface the reduction in metallization becomesnegligible so the pile surface to the volume must be less as possible
HBI has a much more dense structure and lower surface area
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DR
Igangue
andpow
ercons.
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Scrap Classification
SOURCES OF STEEL SCRAPThe iron and steel industry recycles three types of scrap:
home, new, and old scrap.
Home ScrapHome scrap is internally generated in the steel production
process when steel mills and foundries manufacture new
steel products. This form of scrap rarely leaves the steel-making production area. Instead, it is returned to the furnace
on site and melted again. Technological advancements have
significantly reduced the generation of home scrap
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New Scrap
New scrap (also called prompt or industrial scrap) is generatedin steel-product manufacturing plants and includes such itemsas turnings, clippings and stampings leftover when a part ismade during manufacturing processes. This material is typicallysold to the scrap metal industry that processes it for sale tosteel mills and foundries.
Old Scrap
Old or post-consumer scrap results when industrial and
consumer steel products (such as, automobiles, appliances,
buildings, bridges, ships, cans, railroad cars, etc.) have servedtheir useful life. A major challenge in recycling scrap is to
maintain the quality of steel products and minimize
contamination with other metals. Potential residual element
contamination may come from the recycling of automobiles and
municipal scrap
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Scrap handling and preparation
A)Safety: All grades shall exclude:
Pressurized, closed or insufficiently open containers of all originswhich could cause explosions. Containers shall be considered as
insufficiently open where the opening is not visible or is less than 10
cm in any one direction;
Dangerous material, inflammable or explosive, fire arms (whole or
in part), munitions, dirt or pollutants which may contain or emit
substances dangerous to health or to the environment or to the steel
production process;
Hazardous radioactive material:
Material presenting radioactivity in excess of the ambient level of
radioactivity. Radioactive material in sealed containers even if no
significant exterior radioactivity is detectable due to shielding or
due to the position of the sealed source in the scrap delivery.
B) St il ( l )
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B) Steriles (cleanness)
All grades shall be free of all but negligible amounts of other non
ferrous metals and non metallic materials, earth, insulation,
excessive iron oxide in any form, except for nominal amounts of
surface rust arising from outside storage of prepared scrap undernormal atmospheric conditions.
All grades shall be free of all but negligible amounts of
combustible non metallic materials, including, but not limited torubber, plastic, fabric, wood, oil, lubricants and other chemical or
organic substances. All Scrap shall be free of larger pieces (brick-
size) which are non-conductors of electricity as tires, pipes filled
with cement, wood or concrete.
All grades shall be free of waste or of by-products arising from
steel melting, heating, surface conditioning (including scarfing)
grinding, sawing, welding and torch cutting operations, such slag,
mill scale, bag house dust, grinder dust, and sludge.
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C) RESIDUAL AND OTHER METALLIC ELEMENTS
Copper
All grades shall be free of visible metallic copper which
means free of copper wound electric motors, sheets andcopper coated materials, bearing shells, winding, and
radiator cores. All grades shall be free of all but negligible
amounts of wire, insulated wire and cable tubing and other
copper, brass items mixed with, attached to, or coatingferrous scrap.
All grades shall be free of material with high dissolved
copper content such as rebars and merchant bars which will
be grouped in the high residual grades.
Tin
All grades shall be free of tin in any forms such as tin cans,
tin coated materials etc. as Well as bronze elements such as
rings, bearing shells etc.
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Lead
All grades shall be free of lead in any forms such asbatteries, solder, wheel weights, Terne plate, cable ends,
bearings, bearing shells etc.
Chromium, Nickel, Molybdenum
All grades shall be free of alloyed steels and stainless
steels as well as of mechanical Parts (which mainlycontain these elements) such as motors, drive gears for
trucks, Axles, gear boxes, gear wheels, tools and dies as
well as non magnetic pieces
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Scrap Quality Before Loading Into an EAF
Scrap grade characterization is of high importance, not
only to control the liquid steel composition, but also to
ensure reliable melting conditions. Scrap must be layered
inside the basket according to its size distribution and density ina way to allow rapid formation of a liquid pool of steel in the
EAF vessel, while providing protection for the sidewalls and
roof from arc radiation
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Graphite Electrodes
Graphite electrodes play an important part in electricarc furnace operation, allowing for the transfer of
electrical energy from the power supply to the
furnace bath.
- Electrodes must be capable of withstanding large
temperature swings during furnace operation while at
the same time providing for continuous and uniformpower supply to the process.
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Requirements for Graphite Electrodes
1. Good electrical conductivity in order to withstand the high
current density required by the metallurgical process
2. High thermal conductivity to minimize the temperaturedifferences inside the electrodes when in use and, consequently,
to reduce internal stresses
3. Low thermal expansion resulting in high thermal stressresistance
4. Strength at high temperatures to withstand the stresses whenin use
5. Chemical inertness and non-wetting to glass and most metals
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Graphite Structure
G hit El t d M f t i
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Graphite Electrodes Manufacturing
Production
time ~ 3-4months
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Mixing and Extrusion
The milled coke (for graphite electrode primary needle
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- The milled coke (for graphite electrode primary needle
coke is used) is mixed with coal tar pitch and some
additives to form a uniform paste.
-This is brought into the extrusion cylinder.
(In a first step the air has to be removed by pre-pressing.
Than the actual extrusion step follows where the mixture
is extruded to form an electrode of the desired diameterand length.)
- To enable the mixing and especially the extrusion
process the mixture has to be viscous. This is achievedby keeping it at elevated temperature of approx. 120C
(depending on the pitch) during the whole green
production process
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Baking
Two types of baking furnaces :
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Two types of baking furnaces :
- Car bottom furnace:
Here the extruded rods are placed in cylindrical stainless steel
canisters (saggers). To avoid the deformation of the electrodes
during the heating process the saggers are also filled with aprotecting covering of sand. The saggers are loaded on railcar
platforms (carbottoms) and rolled into natural gas- fired kilns.
Ring furnace:Here the electrodes are placed in a stone covert cavity in the
bottom of the production hall. This cavity is part of a ring system
of more than 10 chambers. The chambers are connected
together with a hot air circulation system to save energy. Thevoids between the electrodes are also filled with sand to avoid
deformation. During the baking process, where the pitch is
carbonized, the temp. has to be controlled carefully because at
the temp. up to 800C a rapid gas build up can cause crackingof
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Due to the out gassing during the baking process
the electrode is porous with a low density.
Therefore an impregnation step is added wherethe electrode is loaded with up to 13% of
pitch, which is carbonized in another rebaking
process step.
Impregnation and Rebaking
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Impregnation and Rebaking
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Electrode Shipping
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Electrode Wear Mechanisms
1 Milling and mixing of petroleum needle coke with coal tar
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1. Milling and mixing of petroleum needle coke with coal tar
pitch and selected additives.
2. The mixture is then extruded and cut to cylindrical, green
electrode sections.
3. The green electrodes are placed in saggers which are
moved into large gas fired car bottom kilns where the green
electrodes are baked to approximately 800C.
The bituminous, green electrode material is transformed into
amorphous, brittle carbon which is abrasive and difficult to
machine.
This process requires careful control to ensure that thermal
gradients remain small and rapid gas buildup does not occur..
For this reason, bake cycles are long and take between three tofour weeks
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4. The baked carbon sections are impregnated with petroleum pitch in
order to increase strength and density. This also improves the end
product electrical conductivity.
5. The impregnated carbon sections are again loaded into car bottom
kilns and rebaked so that the petroleum pitch is converted to carbon.
6. The re-baked carbon loaded into large, electrically powered
graphitizing furnaces. Direct current of more than 100kA is passed
through the electrode columns heating them to approximately 3000C.
The intense heating causes the crystalline structure to change from the
random amorphous form to the ordered layer structure of graphite. Thismodification increases machinability of the material as well as greatly
improving electrical, thermal and mechanical properties. The
graphitizing process is very energy intensive and requires more than
3000 kWhr per ton of graphite.
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7. Finally, the graphitized sections are machinedto the required diameter and length on largelathes. Tapered sockets are machined into eachend to accommodate screw in connecting pins
which are used to attach the electrode sectionsend-to-end.
The total production process from extrusion to
shipping is quite time consuming and takesapproximately three months.
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Electrode Consumption
where
CTIP = graphite tip consumption (kg/ton)
RSUB = sublimation rate (kg/kA2 per hr)=average sublimation rate = 0.0135tPO = power-on time (hrs)
I =current per phase (kA)
P = furnace productivity (tons/heat)
P = productivity (tons/hr)
TU = time utilization = tPO /tTAP
or emphasizing the importance of productivity in tons per hour:
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Original Bowman Correlations
CSIDE = graphite sidewall consumption (lbs/ton)
ROX =oxidation rate (kg/m2 per hr)=average oxidation rate = 8 kg/m2 per hr
AOX =oxidizing electrode surface area = DAV LOX (m2)tTAP =tap-to-tap time (hrs)
P =furnaceproductivity (tons/heat)With optimum water cooling the oxidizing length, LOX, is close to the length of the
column inside the furnace at flat bath. This increases with furnace size and is
typically in the 24 m
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Oxidation Rate
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Tip Angle
Variation of Tip Angles between Furnaces
Arc blowout, the cause of tip angling, is a magnetic
phenomenon. It depends on the proximity of the electrodes,
i.e. pitch circle diameter (PCD), the distribution of theferromagnetic scrap and the current distribution within the
charge, between the arcs. It has also been suggested that
deep, foaming slag can offer magnetic field protection. For a
given current, the parameters which can generate low or high
magnetic fields in the arc regions can be summarized in
Table 10.2
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Dependence of Tip Consumption Rate on Tip Angle Forladlefurnaces, increasing tip consumption rate with shorterarcs can be explained by the dissolution of graphite dueto splashing by the liquid steel. In the case of meltingfurnaces, the geometry of the arcing volume around theelectrode tip illustrates that for a given average arcvoltage the lower part of the tip comes closer to theliquid as the angle increases. Thus, at a tip angle of 40the gap between graphite and steel is only about twoinches at an average arc of 200 volt. In contrast, at 25it is over three inches at 200 V.
At 300 V the corresponding gaps are about five inchesand seven inches respectively. The probability ofgraphite contact with steel is therefore increased withgreater tip angles and lower arc voltages.
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SteelSteel
MakingMaking
Material and Steel Analysis
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Material C% Mn % Si% P % S% Cu%
Pig Iron 4 01 1.2 0.2 0.05 0.03
Scrap 0.2 01 0.5 .02 .02 0.25
DRI 2 - - 0.05 0.05 0.03
HBI .75 - - 0.05 0.05 0.03
Product 0.045 0.20 0.03 0.010 0.0005 0.10
Material and Steel Analysis
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EAFEAF
SteelmakinSteelmakin
ggMaximum production withhigh quality and lowest
possible cost
EAF
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EAF
Carbon arc by Sir Hymphrey Davy in the U.S. in1800.
Practical application began (also in the U.S.) with
the work of Sir William Siemens, who was the first
man to melt steel with electric current in 1878-79.
Electric arc furnace are usually characterized by
the maximum capacity of steel in tonnes, power
input capacity (MVA), electrical supply (three
phase AC or DC
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EAF Bottom Shell
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EAF Bottom Shell
EAF Purging System
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EAF Purging System Significantly improved heat and mass transfer
More effective desulphurization anddephosphorization
Lower hydrogen, nitrogen and oxygen content
Balanced carbon-oxygen ratio
Unexpected boiling and rising is prevented More effective melting of the pellets and
briquettes
Improved thermal and chemical homogenization Increased production through reduced meltingtimes
Optimized energy consumption.
Power
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transformation
from high
voltage line tothe arc furnace
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Tran
sform
er
Vr/Vs=Nr/Ns=As/Ar
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DeltaConne
ction
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TapChanger
Electrode Regulation
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As the arc length is dependent on the level of scrap or
liquid under the electrode, and this level changesthrough the heat, it is necessary to have an automatic
control over electrode position.
It is the regulation system which influences many
important aspects of furnace performance, such as
MW input, mean current, arc stability, scrap melting
pattern, energy losses to water-cooled panels,energy, and electrode and refractory consumptions.
Electrode Regulation
Electrode Regulation
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Electrode Regulation
Electrode Regulation
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Oil Flow control is achieved by displacement of the
spool over a stroke in the range of 10 mm. It is
pushed by an hydraulic amplifier. An electrical
signal enters this amplifying valve at the level ofmilliamps. Thus the system consists of a low power
electrical signal, amplified by a hydraulic valve
causing displacement of the main spool valve.
Electrode Regulation
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H
ydraulicRegu
lator
Method for Forming Control Signal
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Method for Forming Control Signal
EAF Voltage and Current
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EAF Voltage and Current
Electrode Column
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-Electrode control performance is limited by the lowest natural
frequency in the positioning system.
-It is therefore very important to ensure sufficient stiffness in the
columns with respect to torsion and bending.
-the main objective is to avoid friction in the roller system while
arranging the roller design to be compact yet rigid. It is important tonote that each arm must be capable of individual movement to allow
for electrode regulation.
-The conventional design uses a hydraulic cylinder to move the
swing column.
-Typical maximum electrode speed is approximately 3035 cm per
second when operating in automatic arc regulation mode. When
operating in manual raise/lower mode the maximum speed is usually
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Module System
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Module System
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ECCJECCJ
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Chemical Energy
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Chemical Energy
C + O CO + 2.75KWh/Nm3 O2
CO + O CO2 + 7KWh/Nm3 O2
C + O2 CO2 + 4.88KWh/Nm3 O2
CH4 + 2O2 CO2 + 2H2O + 8800Kcal/Nm3 CH4
Skull Formation
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Skull Formation
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EAF Charging and Melting
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EAF Charging and Melting
EAF Melting
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EAF Melting
EAF Refining and Tapping
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EAF Refining and Tapping
EAF Process
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EAF Charging
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g g
Steel Reaction
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Steel Reaction
Slag Reaction
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Slag Reaction
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EAF Arc and Foaming slag
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EAF Arc and Foaming slag
Foaming Slag
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g g
Slag flow rate- Q=400-500 kg/minSlag flow rate- Q=100 kg/min
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