copy of steel making shoukery

8/6/2019 Copy of Steel Making Shoukery

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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.




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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.



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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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