1. 1. 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 CVS MAKINA N. SAN. ve TC. LTD. T. Dilovas Organize Sanayii Blgesi 3. Ksm Muallimky Cad. No:21 Gebze 41400 KOCAEL / TURKEYTel. +90 262 759 15 05 Fax. +90 262 759 18 80 www.cvs.com.trcvs@cvs.com.tr
2. 2. 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 4100C, 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.CVS MAKINA N. SAN. ve TC. LTD. T. Dilovas Organize Sanayii Blgesi 3. Ksm Muallimky Cad. No:21 Gebze 41400 KOCAEL / TURKEYTel. +90 262 759 15 05 Fax. +90 262 759 18 80 www.cvs.com.trcvs@cvs.com.tr
3. 3. Induction FurnaceInduction 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 operationof 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.CVS MAKINA N. SAN. ve TC. LTD. T. Dilovas Organize Sanayii Blgesi 3. Ksm Muallimky Cad. No:21 Gebze 41400 KOCAEL / TURKEYTel. +90 262 759 15 05 Fax. +90 262 759 18 80 www.cvs.com.trcvs@cvs.com.tr
4. 4. 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:TitleUnit 0.15Ton 0.3Ton0.5Ton 1Ton1.5Ton 2Ton 3Ton Equipment Kw 100160 250 500 750 1000 1500 rating power InputV 380380 380660380 660380 660380 575-1250 Voltage Melting rate Kg/hour 160300 4901120 16802300 3300 Equipmentton/hour 55 8 10 22 28 35 water rate Equipmentkwh/ton 850800 750 700 650650650 power rate FurnaceV 7507501500 1400-2500 1400-25001400-2500 2300-2500 rating power Furnace rating Ton0.150.3 0.511.52 3 capacity match coverKVA125-160 160-200250-315500-630 800-1000 1000-1250 1600-2000 Transformer Rating 'C1250 125012501250 12501250 1250 Temperature CapacitorKvar 4000 6000800016000 32000 24000 48000 32000 64000 48000 CVS MAKINA N. SAN. ve TC. LTD. T.Dilovas Organize Sanayii Blgesi 3. Ksm Muallimky Cad. No:21 Gebze 41400 KOCAEL / TURKEYTel. +90 262 759 15 05 Fax. +90 262 759 18 80 www.cvs.com.trcvs@cvs.com.tr
5. 5. Electric Arc FurnaceArc 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.CVS MAKINA N. SAN. ve TC. LTD. T. Dilovas Organize Sanayii Blgesi 3. Ksm Muallimky Cad. No:21 Gebze 41400 KOCAEL / TURKEYTel. +90 262 759 15 05 Fax. +90 262 759 18 80 www.cvs.com.trcvs@cvs.com.tr
6. 6. 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 . 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 controlControl 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.CVS MAKINA N. SAN. ve TC. LTD. T.Dilovas Organize Sanayii Blgesi 3. Ksm Muallimky Cad. No:21 Gebze 41400 KOCAEL / TURKEY Tel. +90 262 759 15 05 Fax. +90 262 759 18 80 www.cvs.com.trcvs@cvs.com.tr
7. 7. 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, andflats. 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 maymake bars or strip product.CVS MAKINA N. SAN. ve TC. LTD. T. Dilovas Organize Sanayii Blgesi 3. Ksm Muallimky Cad. No:21 Gebze 41400 KOCAEL / TURKEYTel. +90 262 759 15 05 Fax. +90 262 759 18 80 www.cvs.com.trcvs@cvs.com.tr
8. 8. COMPARISONWhen 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 MaterialsA 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 CVS MAKINA N. SAN. ve TC. LTD. T. Dilovas Organize Sanayii Blgesi 3. Ksm Muallimky Cad. No:21 Gebze 41400 KOCAEL / TURKEYTel. +90 262 759 15 05 Fax. +90 262 759 18 80 www.cvs.com.trcvs@cvs.com.tr
9. 9. 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.ElectricityBecause 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.ProductivityThanking 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, majorCVS MAKINA N. SAN. ve TC. LTD. T. Dilovas Organize Sanayii Blgesi 3. Ksm Muallimky Cad. No:21 Gebze 41400 KOCAEL / TURKEYTel. +90 262 759 15 05 Fax. +90 262 759 18 80 www.cvs.com.trcvs@cvs.com.tr
10. 10. 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 DisposalThe 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 directlyMaintenance 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 OtherCVS MAKINA N. SAN. ve TC. LTD. T. Dilovas Organize Sanayii Blgesi 3. Ksm Muallimky Cad. No:21 Gebze 41400 KOCAEL / TURKEYTel. +90 262 759 15 05 Fax. +90 262 759 18 80 www.cvs.com.trcvs@cvs.com.tr
11. 11. 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 InvestmentIn 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.CVS MAKINA N. SAN. ve TC. LTD. T. Dilovas Organize Sanayii Blgesi 3. Ksm Muallimky Cad. No:21 Gebze 41400 KOCAEL / TURKEYTel. +90 262 759 15 05 Fax. +90 262 759 18 80 www.cvs.com.trcvs@cvs.com.tr
12. 12. 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 companys 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 qualityCast steel grades prone to form defects caused by nitrogen or hydrogen may pose a problem when melted in induction furnaces.CVS MAKINA N. SAN. ve TC. LTD. T.Dilovas Organize Sanayii Blgesi 3. Ksm Muallimky Cad. No:21 Gebze 41400 KOCAEL / TURKEY Tel. +90 262 759 15 05 Fax. +90 262 759 18 80 www.cvs.com.tr cvs@cvs.com.tr
13. 13. 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 FurnaceCVS MAKINA N. SAN. ve TC. LTD. T. Dilovas Organize Sanayii Blgesi 3. Ksm Muallimky Cad. No:21 Gebze 41400 KOCAEL / TURKEYTel. +90 262 759 15 05 Fax. +90 262 759 18 80 www.cvs.com.trcvs@cvs.com.tr
14. 14. Following table gives the operational cost comparison:CALCULATED UNIT EAF (UNIT EAF (PRICE IMF (UNIT IMF (PRICE 30 TON FURNACE CAPACITY PRICE CONS.) CONS.) CONS.)CONS.)ELECTRICITY KWH/TON 0,0967 380 36,75575 55,60ELECTRODESKG/TON 4,91,67,84 0 -OXYGENNM3/TON 0,0830 2,40 0 -NATURAL GAS NM3/TON 0,1 20,20 0 -LIMEKG/TON 0,07 35 2,45 352,45REFRACTORYKG/TON 0,732,10 3 2,10YIELD %1500,89 133,50 0,89133,50POWER-OFF TIMEmin 15 -25-POWER-ON TIME min 35 -55- TOTAL OPERATIONAL COSTUSD/TON 185,24193,65 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.CVS MAKINA N. SAN. ve TC. LTD. T. Dilovas Organize Sanayii Blgesi 3. Ksm Muallimky Cad. No:21 Gebze 41400 KOCAEL / TURKEYTel. +90 262 759 15 05 Fax. +90 262 759 18 80 www.cvs.com.trcvs@cvs.com.tr