Electric Arc Furnace

Electric Arc Furnaces (EAFs) are a central part of the production route that is an alternative to the dominant BF-BOF route. EAFs are used to produce carbon steels and alloy steels primarily by recycling ferrous scrap. In an EAF scrap and/or manufactured iron units – such as DRI, pig iron, iron carbide – is melted and converted into high quality steel by using high-power electric arcs formed between a cathode and one (for DC) or three (for AC) anodes (Worrell et al., 2010. p. 14). Scrap is by far the he most important resource, accounting for about 80% of all electric arc furnace metal feedstock (IEA, 2007. p. 128).

The iron units are loaded in a basket together with limestone – for slag formation – and charged into the furnace. The main task of most modern EAFs is to convert the solid raw materials to liquid crude steel as fast as possible and then refine further in subsequent secondary steelmaking processes. Nevertheless, if time is available, almost any metallurgical operation may be performed during flat bath operation period (after melting), which is usually performed as a pre-treatment to the secondary steelmaking operations. Oxygen and coal powder injection are common treatment operations. (Worrell, et al., 2010. p. 14; Steeluniversity.org)

Total theoratical energy required to melt the scrap and to superheat it to the typical tap temperatures requires around 350 – 370 kWh/t-steel. This energy can be provided by the electric arc, from fossil fuel injection or oxidation of the scrap feedstock. In practice, the energy use is highly dependent on product mix, local material and energy costs and is unique to the specific furnace operation. Factors such as raw material composition, power input rates and operating practices – such as post-combustion, scrap preheating – can greatly influence the balance. Actual electricity use in EAFs are reported to range between 300 – 550 kWh/t, and in 1999 reached an average level of 425 kWh/t. Based on 2005 Figures, IEA estimated that reducing the average electricity consumption from 425 kWh to 350 kWh for every ton of steel produced in EAFs worldwide, 0.1 EJ of energy can be saved annually (IEA, 207. pp. 130-131).

Electric Arc FurnaceSchematic

Electric Arc FurnaceTechnologies & Measures

Technology or MeasureEnergy Savings PotentialCO2 Emission Reduction Potential Based on LiteratureCostsDevelopment Status
Improved Process Control (Neural Networks)

Electricity savings of 30 kWh/t-steel are estimated, and values may change based on scrap and furnace characteristics. (APP, 2010. p. 79)

Emissions reduction potential of the technology is 17.6 kg CO2/t-steel (US EPA, 2010. p.11).

Commercial
EAF Controls

This technology results in 14% reduction in electricity consumption. Additionally a 6% reduction in natural gas consumption were achieved all together.

Direct and indirect CO2 emissions reduction potential of the technology is 34 Kton/year.

An Investment of €3.8 Million over two years aimed at energy savings was made.

Commercial
Oxyfuel Burners/Lancing

2–3 kWh/t-steel of energy can be saved for every minute of heating time reduced;
Electricity savings 0.14GJ/t-steel, with typical oxygen injection rates of 18 Nm3/t-steel.(APP, 2010. p. 80).

US flag Emissions can be reduced by 23.5 kg CO2/t-steel.

Retrofit capital cost for a 110t capacity EAF is $4.8/t.
Due to reduced tap-to-tap time of around 6%, annual savings of $4/t have been realized (APP, 2010. p.80).

Commercial
Flue Gas Monitoring and Control

Electricity savings of 0.05GJ/t-steel are estimated by using this technology (US EPA, 2010. p. 11) . 

Chemical energy recovery rate from exhaust gases can be increased by 50% by adjusting oxygen injection levels for post-combustion based on real time CO and CO2 readings in flue gases, instead of using preset values (Worrell, et al., 2010. p. 90). 

US flag A specific post combustion control system installed in two plants in Mexico and the US lead to reductions of 2% and 4% in electricity consumption, 8% and 16% in natural gas consumption, 5% and 16% in oxygen use, 18% and 18% in carbon charged and injected (Worrell, et al., 2010. p. 90). 

Emissions reduction potential of the technology is estimated to be 8.8 kgCO2/t-steel (US EPA, 2010. p. 11).

Retrofit capital cost are estimated at $3.1/t-steel (US EPA, 2010. p. 11).

The monitoring system installed in Mexico and the US resulted in yield improvements between 1% and 2%, decreased electrode consumption between 3.5% and 16%, increased productivityby 8%. 

Commercial
Post Combustion Optimization in Steelmaking

Energy requirement for BOF reduces by 30%. 50 to 100 kWh/tonne of steel electricity reduction in EAF is estimated.

CO is combusted to produce CO2 and the energy.

Commercial
Hot DRI/HBI Charging to EAF

Charging hot DRI at temperatures up to 600 °C rather than cold DRI results in a melting energy reduction of 150 kWh/t-steel (>0.5 GJ/ton).

Environmental emissions are lower due to energy savings.

Commercial
Foamy Slag Practices

The net energy savings are estimated at 6-8 kWh/t-steel (Worrell et al., 2010. p. 93).

US flag Emissions reduction of 10.6 Kg CO2/t-steel  is estimated (US EPA, 2010).

Retrofit capital cost is estimated at $15.6/t-steel (US EPA, 2010).

Commercial
Scrap Preheating

Scrap preheating can save 0.016 to 0.2 GJ/t-steel. 

Commercial
Bottom Stirring/Stirring Gas Injection

Electricity savings can vary between 12 to 24 kWh, or 0.07 GJ, per ton of steel. 

Emissions saving potential of the technology is 11.7 kg CO2/t-steel.

Retroftit capital cost is $0.94/t-steel.

Commercial
Shaft Furnace Scrap Preheating

With single shaft furnace upto 77kWh/t-steel of electric energy can be saved. Finger shaft furnace allows savings up to 110 kWh/t-steel, which is approximately 25% of the electricity input (Worrell et al., 2010. p. 95).

US flag Emissions are reduced by 35 kg CO2/t-steel.

Retrofit costs were estimated to be $9.4/t-capacity for an existing 100 tonfurnace. Production cost savings may amount $6.7/t-steel. The payback time is estimated as one year. (US EPA, 2010. p.36)

Commercial
Tunnel Furnace Preheating – CONSTEEL Process

Electricity savings are estimated to be 60 kWh/t for retrofits or 0.22GJ/t-steel. 

Emissions reduction of 35.5Kg CO2/tonne steel is achievable.

Investment costs were estimated to be $3.2 million 500,000 t/y, or $7.8/t-steel. Annual costs savings were estimated to be $3.0/t-steel. The payback time is estimated as 1.3 years. (US EPA, 2010. p. 36)

Commercial
Direct Current (DC) Arc Furnace

Net energy savings over older AC furnaces are estimated to be 0.32GJ/t-steel. Compared to new AC furnaces, the savings are limited to 0.036-0.072 GJ/t-steel (US EPA, 2010. p.35). 

Emissions reduction potential of the technology is 52.9 Kg CO2/t-steel (US EPA, 2010. p.11).

The additional investment costs over that of an AC furnace are approximately $6.1/t capacity. The payback time is estimated as 0.7 years (US EPA, 2010. p.35).

Commercial
Waste Heat Recovery for EAF

Approximately 130 kWh/t-s of energy can be recovered (efficiency 30%).
If recovered energy is used for power generation with saturated steam 2.8 MWh/y of electricity can be generated.
If the recovered energy is used for power generation with superheated steam,  15.1 MWh/y of energy can be generated.  (For an EAF melting 150 t/charge of DRI with tap-to-tap time of 49 mins, and power on time of 40 mins) (JASE-W, 2012)

If recovered energy is used for power generation with saturated steam, corresponding CO2 emission reduction will be 12,600 t/y;
If recovered energy is used for power generation with superheated steam, corresponding CO2 emission reduction will be 73,400 t/y. (For an EAF melting 150 t/charge of DRI with tap-to-tap time of 49 mins, and power on time of 40 mins) (JASE-W, 2012)

Research
Airtight EAF Process

Energy savings are estimated to be around 110 kWh/t-steel (Worrell et al., 2010. p. 95)

Significant emissions reduction can be expected due to reduction in energy consumption.

Commercial
Adjustable Speed Drives (ASDs)

Total fan energy consumption can be decreased by 67%. Electricity savings are estimated to be 16.5 kWh or 0.06 GJ per ton of steel.

Decreased energy consumption will lower emissions.

Retrofit capital costs are $2/tonne steel. The payback time is estimated as 2 to 3 years.

Commercial
Comelt

Reduction of energy consumption of approximately 100 kWh/tonne is expected compared to the conventional EAF.

 

Reduced energy consumption will eventually result in reduced emissions.

Maintenance costs would decrease due to a simpler plant design.

Commercial
Contiarc Furnace

Energy losses are reduced by 220 kWh/t-steel as compared conventional furnace systems. Also electric power consumption reduces by 25 kWh/t-steel (0.091 GJ/t) due to reduced flue gas amount requiring cleaning. 

Waste gas and dust volumes are considerably reduced by the technology.


 

Commercial
Twin-Shell DC Arc Furnace

Electricity savings are 0.068GJ/t-steel.

Emissions reduction potential of the technology is 11.1KgCO2/t-steel.

Retrofit capital cost is $9.4/t-steel over that of a single-shell furnace. The payback time is estimated as 3.5 years..

Commercial
Post Combustion of EAF Flue Gas

For a particular post-combustion system, electricity savings ranged from 6 to 11% depending on the operating conditions (Worrell et al., 2010. p. 93).

Energy savings will result in reduced emissions.

In a particular application tap-to-tap times were decreased by 3 to 11% depending on operating conditions (Worrell et al., 2010. p. 93)

Commercial
Engineered Refractories

Savings of 11kWh/-steel are expected by applying this technology.

Energy savings will result in reduced emissions.

Commercial
Eccentric Bottom Tapping

Electricity savings of 0.05GJ/t-steel are estimated by using this technology.

Emissions reduction of 8.8 Kg CO2/t-steel are expected.

Retrofit capital costs are $5.0/t-steel.

Commercial
ECOARC

This furnace consumes 200 kWh/ton power at oxygen injection rate of 40Nm3/ton.

Flexibility of scrap mixing reduces the costs for the process. Electrode consumption is as low as 0.8-1.0 kg/ton.

Demonstration
Ultra High Power (UHP) Transformers

Electricity savings are estimated to be 1.1 kWh/t-steel for every MW power increase.
Power consumption dropped by 11 and 22kWh/t respectively for 2 furnace lines when operating voltage increased from 600V to 660V in one furnace and from 400V to 538V in another (Worrell et al, 2010. p. 91). 

US flag Emission reductions are estimated to be in the range of 10 kg/t-steel (US EPA, 2010. p. 11).. 

To increase the operating voltage  from 600V to 660V in one furnace and from 400V to 538V in another a $1.1 million investment was made (Worrell et al, 2010. p. 91). 

.Capital costs were estimated to be $3.9/ton ($4.3/tonne). The payback time is estimated as 5.2 years (US EPA, 2010. p. 33).

 

Commercial
Used Tires for Insulation in EAF

Electrical energy consumption to produce one tonne of billet was reduced from 424 kWh to 412 kWh.

CO2 savings were equivalent to the removal of approximately 4,000 cars from the road.

Using rubber tyres, steelmaking costs are 80% of what they were when using coking coal.

Demonstration
New-Scrap Based Steelmaking Process using Primary Energy

About 32% reduction of primary energy Intensity for liquid steel production compared to the conventional EAF is expected by this technology.

Depending on the CO2 emission of the electricity grid, the significant amount of CO2 emission will also be reduced.

There will about 19% reduction in the energy cost per tonne of liquid steel produced.

Demonstration
Injection of Aluminium instead of Ferrosilicon for Stainless Steel Making in EAF

Electrical energy demand was significantly decreased by approximately 10%.

Reduction in emissions because CO is not let to oxidize rather it foams the slag.

Cost decreases due to savings in alloying agents such as Cromium.

Research
Model Based Steel Temperature Measurement

Energy savings are achieveable by the implementation of this technology.

There will be related CO2 emission reduction.

Evaluation of attainable savings will be performed on the basis of energy balance of whole process.

Research
Optimal Charge Calculation in EAF

Energy-Optimal charging of scrap by using this technology.

This technology is expected to bring savings of 5 – 10 % in scrap costs.

Commercial
Holistic Quality Driven Production Control

The technology reveals significant saving potential in terms of energy.

Cost savings are obtained due to on-line monitoring of the amount of alloying agent.

Demonstration
Dynamic Asymmetrical Control of AC EAF

The melting rate was Improved by as much as 8 % by increasing the mean electric power Input and by shortening the power-off times.

The economical mode of operation reduces the consumption of refractory gunning mixes by around 10 %.

Commercial
Hydrogen and Nitrogen Control in Ladle and Casting Operations

Better control results in energy savings by an estimated 400 million kilowatt hours (kWh) per year.

CO2 emissions decreases.

Estimated annual savings are $20 million when technology is in widespread commercial use.

Research
Modification of Side Wall Water Cooled Panels and Water Header

This technique increases furnace capacity by 18-20 tonnes. Power consumption was reduced from 800 kWh to 620 kWh/t-steel.

Annual savings of Rs. 864 000 000 were obtained.

Commercial
Development of a process to continuously melt, refine and cast high quality steel

A total of 10% energy savings will occur by reducing the energy needed for auxiliary operations. Savings of 20 kWhr/t in auxiliary energy are reported.

Capital cost for the equipment is $35 million for a 1,000,000 tpy facility.

Demonstration

Electric Arc Furnace Publications

Energy Efficiency Improvement and Cost Saving Opportunities for the U.S. Iron and Steel Industry

The U.S. Environmental Protection Agency’s (EPA) energy guide, Energy Efficiency Improvement and Cost Saving Opportunities for the U.S. Iron and Steel Industry, discusses energy efficiency practices and technologies that can be implemented in iron and steel manufacturing plants. This guide provides current real world examples of iron and steel plants saving energy and reducing cost and carbon dioxide emissions.

Page Number: 

14, 90-96

The State–of-the-Art Clean Technologies (SOACT) for Steelmaking Handbook

 

The State–of-the-Art Clean Technologies (SOACT) for Steelmaking Handbook is developed as part of the Asia-Pacific Partnership on Clean Development and Climate program and seeks to catalog the best available technologies and practices to save energy and reduce environmental impacts in the steel industry. Its purpose is to share information about commercialized or emerging technologies and practices that are currently available to increase energy efficiency and environmental performance. 

Page Number: 

78-93

Global Warming Countermeasures: Japanese Technologies for Energy Savings / GHG Emissions Reduction

This revised 2008 version of the publication from New Energy and Industrial Technology Development of Japan includes information on innovative Japanese technologies for energy efficiency and for the reduction of COemissions.  

Page Number: 

80-84