Comparison Between Imf Eaf

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COMPARISON BETWEEN EAF AND IMF

(D. ERTAS – Project and Contracting Department - CVS MAKINA)

By far, the most important engineering and construction material in the world, steel

application figures prominently in many aspects of human life, from civil structures to

automotive manufacture, from paper clips to refrigerators and washing machines and from

aircrafts to the finest surgical instruments. All major industrial economies have a strong

domestic steel industry which shaped their economic growth in the initial stages of their

development.

Steel is produced either from basic raw materials namely iron ore, lime stone and coke,

using the blast furnace and basic oxygen furnace processes, or from recyclable steel scraps

via the electric arc furnace process or induction melting process. The molten steel is stored

and refined in ladles before being solidified and cast into slabs, blooms, billets and bars by

continuous casting machine and/or ingot casting. Semi-finished steel is re-rolled (formed and

finished) to produce finished steel items like plates, flats, bars, sections, tubes etc of varying

thickness and dimensions.

The High-Frequency induction furnace is widely used to produce tool steel (cast steel). The

melt consists of selected scrap of known carbon content. This is placed in a crucible, which is

surrounded by a water-cooled induction coil. A high frequency alternating current is passed

through the coil and this set up an alternating magnetic field within the melt which

generates intense heat and also has a stirring effect. Not only is it possible to obtain high

temperatures, but the degree of heat may be accurately controlled. The furnace is tilted to

pour out the molten metal. Induction furnace capacities range from less than one kilogram

to twenty tonnes capacity, and are used to melt iron and steel, copper, aluminium, and

precious metals. The one major drawback to induction furnace usage in a foundry is the lack

of refining capacity; charge materials must be clean of oxidation products and of a known

composition, and some alloying elements may be lost due to oxidation (and must be re-

added to the melt).

The electric-arc furnace consists of a large shallow bath with either an acid or basic lining,

carbon electrodes over the hearth which may be raised or lowered. Current is supplied to




these electrodes from special transformers. The hearth is charged with lime to remove the

impurities and form a slag. The metal which forms the melt is scrap steel of known

composition. When the furnace is charged the electrodes are lowered and the current is

switched on. The electrodes are then raised and an electric arc jumps across from the

electrodes to the metal and melting begins. The temperature near to electrode tip reaches

about 4100ºC, which is the heat to melt the scrap. Lime, fluorspar, carbon and Ferro-alloys

are added to de-oxidize the metal. The electric arc furnace can used to produce high grade

alloy steels, HSS, High Tensile Steel and Silver Steel. This is possible because of the greater

control over impurities and thus the steel making. It is increasingly used nowadays in the

production of common steel. Arc furnaces range in size from small units of approximately

one ton capacity used in foundries for producing cast iron products, up to about 400 ton

units used for secondary steelmaking (arc furnaces used in research laboratories and by

dentists may have a capacity of only a few dozen grams).

Following paper aims to give comparison between Electric Arc Furnace Technology with

Induction Melting Furnace Technology.




Induction Furnace

Induction heating process is a method in which the electrical conducting material is heated

through by eddy currents induced by a varying electromagnetic field. The principle of the

induction heating furnace is similar to that of a transformer.

Induction furnace has it's own limitation. The induction process used in foundries lacks

refining capacity. Charge materials must be clean of oxidation products and of a known

composition, and some alloying elements may be lost due to oxidation (and must be re-

added to the melt).

The frequency of operation of

induction furnace also vary. Usually

it depend on the material being

melted, the capacity of the furnace

and the melting speed required. A

high frequency furnace is usually

faster to melt a charge whereas

lower frequencies generate more

turbulence in the metal, reducing

the power that can be applied to the melt.

When the induction furnace operates it emits a hum or whine (due to magnetostriction), the

pitch of which can be used by operators to identify whether the furnace is operating

correctly, or at what power level.




Following are the features of induction furnace:

· Highest chemical durability.

· High refractoriness.

· Available in various sizes.

· Comes in different capacities.

Some parameters of induction furnaces are give in the following table:

Title Unit 0.15Ton 0.3Ton 0.5Ton 1Ton 1.5Ton 2Ton 3TonEquipmentrating power Kw 100 160 250 500 750 1000 1500

InputVoltage V 380 380 380 660 380 660 380 660 380 575-1250

Melting rate Kg/hour 160 300 490 1120 1680 2300 3300Equipmentwater rate ton/hour 5 5 8 10 22 28 35

Equipmentpower rate kwh/ton 850 800 750 700 650 650 650

Furnacerating power V 750 750 1500 1400-2500 1400-2500 1400-2500 2300-2500

Furnaceratingcapacity

Ton 0.15 0.3 0.5 1 1.5 2 3

match coverTransformer KVA 125-160 160-200 250-315 500-630 800-1000 1000-1250 1600-2000

RatingTemperature 'C 1250 1250 1250 1250 1250 1250 1250

Capacitor Kvar 4000 6000 8000 160003200024000480003200064000 48000




Electric Arc Furnace

Arc furnace provides a simple and effective way of melting various grades of scrap and then

going ahead to refine the metal to desired specification. It is also useful in making all kinds

of steels including tool steels and alloy steels. This provides a method of utilising low cost

scrap, which is available in abundance.The key advantage in EAF melting is that refining is

possible and you can also produce low carbon steels.

An electric arc furnace is mainly used for making steel and consist of devices like refractory-

lined vessel and electrodes. Electrodes are normally round in section and comes in segments

with threaded couplings, so that as the electrodes wear, new segments can be added. The

arc forms between the charged material and the electrode. The charge so formed is heated

both by current passing through the charge and by the radiant energy evolved by the arc.

Through automatic positioning system electrodes are raised and lowered. For positioning

electric winch hoists or hydraulic cylinders are used. The regulating system maintains an

approximately constant current and power input during the melting of the charge, even

though scrap may move under the electrodes while it melts. The mast arms holding the

electrodes are used to convey the current to the electrode holders. The transformer is

installed in a vault to protect it from the heat of the furnace.

The refractory lined vessel having a removable roof is separated from the electrical system.

The bottom of the furnace, is lined with refractory bricks and granular refractory material.

There is a tilting platform on which the furnace is built so that the liquid steel can be poured

into another vessel for transport in the steel making process. To prevent the liquid steel from

the contaminants like nitrogen and slag modern furnaces have a bottom tap-hole on the

spout. In some of the latest plant, scrap pre-heating is applied with different method to

decrease the electric consumption and to increase the productivity.

Operation

Scrap metal is delivered to a scrap bay, located next to the melt shop. The furnace is filled

with the scrap. After putting the scrap inside furnace the roof again cover the top of the

furnace where the melt down goes on.




The electrodes are lowered onto the scrap, an arc is struck and the electrodes are then

pushed into the layer of shred at the top of the furnace. Voltage selected for this level of

operation is usually small. Low voltages protect the roof and walls from excessive heat and

damage from the arcs.

After reaching the base of the furnace and the electrodes can be raised slightly, thereby

increasing the length of the arcs and increasing power to the melt. This helps in the

formation of molten pool even more rapidly. Modern furnaces are designed with some

additional features. In this oxygen is pushed into the scrap. sometimes chemical heat is

provided by wall-mounted oxy-fuel burners. Both processes accelerate scrap meltdown.

The formation of slag is an important part of steel making which floats on the surface of the

molten steel. Slag not only acts as thermal blanket but also reduce erosion of the refractory

lining. For a furnace with basic refractories causes the slag to foam, allowing greater thermal

efficiency, and better arc stability and electrical efficiency.

Once srap has been completely melted down, often another bucket of scrap is charged into

the furnace and melted down. After the second charge is completely melted, refining

operations take place to check and correct the steel chemistry and superheat the melt above

its freezing temperature in preparation for tapping. Once the temperature and chemistry are

correct, the steel is tapped out into a preheated ladle through tilting the furnace.

Alternating current furnaces have three moving graphite electrodes. Heating and melting of

metal is enabled by radiant energy of the arc burning between the electrodes and metal, and

the temperature in the arc zone reaches 4000 °С. The uniform burning of arc is regulated by

means of moving of current-carrying electrodes transversely to the surface of the melt. It is

possible to regulate the radiant energy by stretching and contracting the arc with two

moving electrodes.

Principles of control

Control of electrode movement is, in its turn, based on maintaining of constant level of the

burning electric arc external impedance. During the previous decade they have undergone a

drastic change due to the uprise of the new computing techniques generation in the industry

such as controllers and digital controlled electric drives.




The voltage of furnace power transformer may vary in steps via the tap changing device.

But, as a rule, the transformer taps change is not applied in small furnaces during the

technological process.

The problem of electrode failure at arc ignition in up-to-date electric drives is easily solved by

adjusting current limiting set points in the electrode movement controlled by hydraulic

cylinders, and the overcharge alarm is transmitted to the master controller to ensure the

appropriate system response.

With the help of modern automation equipment it becomes possible to integrate the control

system into a top-level network for organization of recording systems of different types,

control or document management systems.

The use of EAFs allows steel to be made from a 100% scrap metal feedstock, commonly

known as 'cold ferrous feed' to emphasise the fact that for an EAF, scrap is a regulated feed

material. The primary benefit of this is the large reduction in specific energy (energy per unit

weight) required to produce the steel.

EAFs can be rapidly started and stopped, allowing the steel mill to vary production according

to demand. Although steelmaking arc furnaces generally use scrap steel as their primary

feedstock, if hot metal from a blast furnace or direct-reduced iron is available economically,

these can also be used as furnace feed.

Applications

Electric Arc Furnace has following applications:

· Electric arc furnace produces many grades of steel.

· Concrete reinforcing bars common merchant-quality standard channels, bars, and

flats.

· Special bar quality grades used for the automotive and oil industry.

· A typical steel making arc furnace is the source of steel for a mini-mill, which may

make bars or strip product.




COMPARISON

When a foundry/meltshop is choosing between state-of-the-art Electric Arc Furnace or

medium frequency coreless induction melting for its operation, the discussion centers on key

factors such as energy costs, environmental regulations, charge materials, labor and

production levels. To perform a proper analysis of what system is best for an operation, all

factors must be quantified in dollars per ton of molten iron and then totaled to determine the

cost-effective melt solution.

This analysis reviews the following factors for both melt systems and assigns them a cost in

dollars per ton of iron:

* charge material/treatment cost;

* operational cost;

* labor cost;

* environmental cost;

* investment and breakeven analysis.

These factors then can be totaled to determine the melt system that is a more cost-effective

option for the specific production situation.

Charge Materials

A major difference between the compared melt processes is the ability to use differing

quality charge materials. Oxidation and reduction reactions take place within and above the

melt zone during electric steelmaking, which allows for the usage of highly oxidized and low

quality scrap material. Induction furnaces are more sensitive to low quality charge materials

and contaminants, resulting in premium scrap costs. A reductive atmosphere is not present

and therefore iron oxide will not be reduced. This increases iron loss through the slag.

Another charge material difference between the melt processes is the cost of alloys and

nonmetallic additions. An induction furnace operation uses a high-grade silicon carbide to




adjust iron chemistry. In addition, pure carbon in the form of graphite is used for

carburization. These additions are costs not required for the EAF.

Electricity

Because of higher electrical energy input with higher electrode current, higher electrical

efficiency with reactors and thanking to additional chemical energy input (nearly 35 % of

total energy) by oxy-fuel burners and C-injection, EAF operation requires lower specific

energy consumption around 380-420 kWh/ton whereas IMF has 680-720 kWh/ton

consumption.

Productivity

Thanking to faster equipment movements, EAF has advantageous for power-of time in one-

heat. Additionally, chemical energy input by supersonic oxygen and carbon injection, power-

on time of EAF is lower. In general, tap-to-tap time of EAF is around 50-60 minutes whereas,

one heat can take 120-150 minutes for IMF. The profitability of any industrial plant increases

and decreases directly with production rates.

Labor

EAF operation with state-of-the-art equipment has the following labor requirements: two EAF

operators, one charge crane operator, one foreman. This results in five workers per shift.

A medium frequency melt system's labor requirements are: two furnace operators, two

charger and crane operators, one supervisor. Five workers per shift are required for melting

within the outlined operation.

Refractory

The EAF is designed for a two-week melt campaign. After the two weeks, the anticipated

repairs would be the breast and tap hole, spout, well and melt zone. In addition, major




replacements and repairs for the spout, well, melt zone and brick lining above the melt zone

must be considered.

For the three medium frequency furnaces, the refractory and labor items to consider are

major furnace relining, general/small furnace repair and pouring spout repair.

The largest differences are in general refractory and small repairs because of the increased

level of materials and man-hours for a three-furnace system. The medium frequency system

does have the advantage of not using a holding furnace, which saves on refractory cost.

Waste Disposal

The wastes accumulating from both systems are slag and dust. The difference lies in the

quantity of waste. EAF generate around 8 % of their melt rate as slag and 20-30 lb of dust

per ton of iron melted. EAF slag from this analysis will have a commercial value for beneficial

reuse.

Medium frequency furnace wastes are less in volume, slag mass is 1% of the melt. This

operation does not produce slag for commercial reuse. In addition, in medium frequency

melting, the dust collected (1 lb/ton melted) in a baghouse requires treatment for leachable

heavy metals.

However, in addition to indirect suction from canopy hood in IMF case, direct suction from

furnace roof fume emission to atmosphere for EAF operation is less due to the chance to

exract the off-gasses from furnace directly

Maintenance

Maintenance costs for both operations are calculated assuming costs for equipment, spare

parts, in-house maintenance and outside contractors and based on reports by foundries.

Costs for the EAF operation are estimated at $6.40/ton of melted iron and $4.40/ton melted

iron for the medium frequency furnace operation.

Buildings and Other




This item includes building operational costs such as electricity and natural gas, office

operation, transportation and safety and is based on reports by foundries. This parameter is

equal for both operations.

Capital Investment

In this analysis, the capital investments for these two systems are based on past projects.

Based on this experience, medium frequency melt systems are installed at a 25% reduced

cost when compared to EAF systems.

For the electric melting system, the major cost factors are the furnaces, charging system,

buildings with power supply and environmental controls.




Which to Choose?

Since it gained prominence in the 1960s, electric melting has been an attractive option for

iron foundries/meltshops. The key is that when the selection of a system is being made, all

the proper data and factors must be considered to ensure the most efficient melt operation.

The temperature of the arc is much higher than the max temperature created by the

induction. A big difference will be the energy costs. Arc is electrically more efficient. Most

coreless induction furnaces are for non-ferrous melting and are much smaller than a small

arc furnace.

EAF practice needs experienced melters and operators who are in short supply. Also the cost

of graphite electrodes and refractories increase the operational cost. Energy cost for melting

compares with Induction furnace. The cost of EAF may be low compared to Induction

furnace, but the cost of electrical transformers,switch gear,cables will be expensive.

Additionally, additional pollution control equipments has to be installed to meet company’s

local laws.

Normally where the liquid metal demand is above 25 tons on a continuous basis, EAF is

installed.

The major drawback in Induction melting is the use of clean and segregated scrap, which is

expensive and the absence of any refining. Installation of the equipment is quick and a low

skilled operator can un the furnace. You are able to produce very low carbon (0.03%) grades

in induction furnace. Also changing grades of steel can be done on a heat to heat basis.

For hot metal requirements below 5 tph, the medium frequency coreless induction furnace

has proven to be the best choice from an operational and economic standpoint.

Dust generation and collection continue to be two serious problems with Induction Furnaces,

and no satisfactory solution appears imminent.

If the refractory and ladle practice is good, arc furnace metal should also be of better quality

Cast steel grades prone to form defects caused by nitrogen or hydrogen may pose a problem

when melted in induction furnaces.




Both types of melting furnace operations benefit from the use of refining operations

(secondary metallurgy), particularly with respect to "clean steel" requirements.

Each melting operation presents its own set of unique requirements, and the optimum

practice must be developed on a case-by-case basis; rules-of-thumb are inadequate.

Due to the nature of Induction Furnace melting process, refining stage cannot be

accomplished. Consequently phosphorus reduction and slag removal cannot be succeeded.

To obtain proper quality, clean from hazardous elements and dirt free scrap should be used.

These kind of scrap is respectively expensive and difficult to find than the ordinary scrap.

Due to the shape of the Induction Furnace, scrap size is very limited. To prepare scrap blend

brings extra cost.

Electric consumption for EAF is very low. Even less than 400 kwh/ton can be quarantined.

Delivery time of the mechanical equipment is approximately 4 months, but electrical

equipment such as step-down transformer, furnace transformer etc. is 8-10 months. This will

be the same as Induction Furnace.

Productivity of EAF is two times more than the Induction Furnace in terms of ton/hour.

The scrap yield is 90% in EAF but as already mentioned on item 1, EAF has opportunity to

use cheaper scrap than the Induction Furnace




Following table gives the operational cost comparison:

CALCULATEDFURNACE CAPACITY 30 TON UNIT

PRICEEAF (UNITCONS.)

EAF (PRICECONS.)

IMF (UNITCONS.)

IMF (PRICECONS.)

ELECTRICITY KWH/TON 0,0967 380 36,75 575 55,60

ELECTRODES KG/TON 4,9 1,6 7,84 0 -

OXYGEN NM3/TON 0,08 30 2,40 0 -

NATURAL GAS NM3/TON 0,1 2 0,20 0 -

LIME KG/TON 0,07 35 2,45 35 2,45

REFRACTORY KG/TON 0,7 3 2,10 3 2,10

YIELD % 150 0,89 133,50 0,89 133,50

POWER-OFF TIME min 15 - 25 -

POWER-ON TIME min 35 - 55 -TOTALOPERATIONAL COST USD/TON 185,24 193,65

Steel production using the electric arc furnace has increased significantly in recent years and

now accounts for a little over one third of total world output.

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Comparison Between Imf Eaf