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Highly Efficient Mini-Mills

with Innovative Scrap Pre-Heating and Direct Rolling of Long Products

St. Fellner1, C. Tercelli1, J. Buttler2

1Primetals Technologies Austria GmbH

Turmstraße 44, Linz, Austria, 4031

Phone: +43 732 6592-5333

Email: stefan.fellner@primetals.com

2Primetals Technologies USA LLC

501 Technology Drive, Canonsburg, State, USA, 15317

Phone: +1 724514 8397

Email: joerg.buttler@primetals.com

Key words: Production cost optimization, Energy efficiency, Resource efficiency, Endless Casting, Endless Rolling, Pre-

Heating Technology, Yield

SUMMARY

The paper discusses recent innovations of Primetals Technologies in the field of micro- and minimills, furnace

technology, casting and rolling technology, which all address the “high efficient minimill” approach enabling a

future-oriented, sustainable steelmaking while saving resources and creating clear added value.

Significant energy savings can be achieved by utilizing state-of-the-art technologies.

Efficient scrap preheating in Quantum EAF results in 20% lower conversion cost for the melting process.

Compact minimill design of the endless type reduces the mill conversion cost by a further 10% and improves yield

by 1.5-2 percentage points.

Use of advanced automation technologies (smart sensors, robots, integrated process control and –optimisation

solutions) improves plant operation and utilization.

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INTRODUCTION

From a global perspective, today’s steel world is slowly returning to the “normal” modus of pre-crisis times. Annual

crude steel production is picking up again, however output growth is dominated by geopolitical and geographical

factors. This is why a spotlight on local peculiarities and developments needs to be cast in order to understand the

trends and behaviors of players in the different regions of the world.

China has taken out more than 100 mtpy of steel production through Induction Furnaces and is yet to remove

another 90 mtpy in the coming years1, replacing them mostly by modern Electric Arc Furnaces at a pace

unprecedented anywhere else in the world.

The US are upgrading their facilities and putting in new ones, owing to the new policies of the current

administration as well as to the fact that cheap overseas imports are attacking their local supply base. On top of this,

steelmaking becomes big in the Next Eleven Countries2 in the attempt to replace imports by local production

(mainly of long products), upgrading the value chain and creating jobs in the basic industry at the same time.

These global megatrends are fueled – and hampered at the same time! – by the fact that steelmaking is an energy

intensive, rather environmentally unfriendly and raw material dependent industry.

The main cost factors are the availability and cost of scrap (and partly of virgin materials as DRI, HBI) and the cost

of electrical energy, which together add up to more than 80% of the conversion cost. Again, China comes into play

when looking at scrap , as local players are setting up EAF facilities in the country, predominantly being fed by

(local?) scrap. Studies3 show that scrap availability will remain at minimum current levels as recycling rates in

China are picking up.

When it comes to long products, being a commodity product abundantly available on the global market place, the

matter it all comes down to is COST: cost of production, cost of transportation,cost of assets and cost of yield loss

are becoming a relevant factor in today’s competition. The winners in the competition will be those able to make

available their goods at their customers’ yard at lowest possible price and shortest possible time.

Leaving out of consideration for this analysis the market dynamics of supply and demand, long-term trading

obligations and futures, respectively, one of the main drivers for price of finished long products is the price of raw

material (predominantly scrap), which most of the producers in the industry need to obey to and are exposed to. At

the same time it serves as a valid indicator for the long products price trend as most of these products are being

produced through non-BOF routes4. Figure 1 gives an overview over the scrap cost development in the last ten

years. In average the scrap market price fluctuated between 200 and 300 Euro.

1 Wu Wenzhang: China Drives World Steel Market Price Rally, Dubai, SteelHome, December 2016 2 Jim O'Neill, Dominic Wilson, Roopa Purushothaman, Anna Stupnytska: How Solid are the BRICs?, Global Economics Paper

No. 134, Goldman Sachs, 1. Dezember 2005 3 See World Steel Dynamics, Publication of AIST March 2014 and McKinsey&Company – 3rd Steel Scrap and Raw Material

Conference, September 2017, Bangkok 4 Except for DR-based facilities for Long Products, predominantly in operation in Middle East

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Figure 1: Scrap Market Price development over the last ten years

Based on these macroeconomic realities and possible geographic market circumstances, producers can excel on the

market only through lowest possible production costs, i.e. conversion costs from raw material to finished product.

It is the intention of this paper to identify optimization potentials through technologies already available on the

market or currently under development, starting from the analysis of conversion cost.

Conversion cost analysis and potential for optimization

The conversion costs are basically a function of electrical and chemical energy, refractory and electrode

consumption, and personnel costs, paired with yield from scrap to product and utilization rates of the facility (net

production time).

Figure 2: Conversion Cost Share/ Cost Drivers; Source: Primetals Conversion Cost Simulation based on Customer Data

(Personnel Cost based on European wages Index 2018)

The steelmaking process accounts for close to 70% of the total conversion cost from scrap to finished product.

Rolling, being a less energy-intensive process, is only accountable for around 10% of the total conversion costs. The

0%

10%

20%

30%

40%

50%

60%

70%

Melting Rolling Auxiliary Facilities Personnel

Conversion Cost Share from Scrap to Product

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auxiliary facilities (mainly water treatment, cranes, electrical substation and SVC, if applicable, oxygen plant, etc)

are a minor contributor.

Costs for maintenance and operational personnel, however, are one of the major cost drivers in developed countries.

Specific cost per ton for personnel is of course highly dependent on the geographical location of the facility and the

underlying local costs for personnel.

Consequently the focus to tackle these challenges has to be tailored to the saving potentials in the different process

steps of production:

- Melting, with focus on energy savings and savings on consumables

- Casting and rolling, with focus on yield and energy consumption

- Manpower, with focus on manpower reduction, automatization, safety and process optimization

Based on above analysis it becomes visible that technological innovations and process optimization yield high

potentials of conversion cost reduction. In the forthcoming sections of this paper the major fields of current

innovation efforts are outlined.

MELTING PROCESS

Enhanced furnace efficiency

The melting process accounts for a major portion of the conversion cost. In particular, electrical energy is the major

cost driver in steel making. Traditional Electrical Arc Furnaces typically consume around 450kWh/t of liquid steel

at an average oxygen consumption of 35 Nm³/t. Recent innovations have been achieved by using the off-heat of the

steel bath to pre-heat the scrap either in shafts sitting above the vessel or through conveyors feeding scrap to the

furnace.

This has led to a drastic decrease of specific electrical energy consumption in the steelmaking process:

Figure 3: Overview of electrical energy consumption of 136 running EAFs in function of Oxygen consumption

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Using state-of-the-art furnace technology, like the Quantum EAF developed by Primetals Technologies, can cut

specific electricity consumption by 20-25% over conventional furnace installations.

The design of the Quantum EAF, with the off-gas passing through the scrap column in the shaft, guarantees the

most efficient scrap preheating and result in 20-30% lower energy consumption compared to conventional EAFs..

Flat-bath operation, typical of the Quantum EAF, increases the efficiency of heat transfer from the electrode and at

the same time minimizes flicker and network disturbances. Thanks to the presence of a significant hot heel, scrap

melting is faster than direct melting with the electric arc. These factors concur to lower the electrode consumption

to a very low 0,9 kg/t (compared to 1,3 kg/t in a conventional EAF). Working with flat bath also reduces the

refractory consumption (actual refractory consumption of the Quantum EAF in operation is 1,5 to 2.0 kg/t of steel,

significantly lower than a conventional EAF.)

Achieving operating cost 20% lower than a conventional, well-performing EAF, the Quantum EAF can quickly pay

back the initial higher capital expenditure.

Quantum EAF Conveyor EAF Conventional EAF

Electrical energy 0,07 US$/kWh 290 kWh/t

20.3 US$/t

320 kWh/t

22.4 US$/t

370 kWh/t

25.9 US$/t

Electrodes 4.4 US$/kg 0.9-1.1 kg/t

4.4 US$/t

0.9-1.1 kg/t

4.4 US$/t

1.3 kg/t

5.7 US$/t

Refractory 1.75 US$/kg 2.0 kg/t

3.5 US$/t

2.5 kg/t

4.4 US$/t

3.0 kg/t

5.2 US$/t

Total 28.2 US$/t 31.2 US$/t 36.8 US$/t

Savings per ton + 3.0 US$/t

+11%

+ 8.6 US$/t

+30%

Annual savings 500,000 tpy 1.5M US$/year 4.3M US$/year

for production of 800,000 tpy 2.4M US$/year 6.9M US$/year

CASTING & ROLLING PROCESS

The development of casting and rolling mill equipment has led to a point where only significant changes in plant

operating mode, rather than incremental design improvements, will lead to substantial gains of efficiency. The last

years have seen a move towards endless rolling operation, taking mainly two forms:

- Semi-endless rolling, where continuous-cast billets, either cold- or hot charged, are welded together into

one continuous strand through the rolling mill

- Endless rolling, where a continuous casting strand is fed into the rolling mill without being cut into billets

The application of one or the other technology is tailored tot he specific targets of each minimill. In general, endless

rolling, with its rigid connection between a high-speed caster and a rolling mill, develops its fullest potential when

producing common steels (typically, straight reinforcing bars). Higher added-value products, characterized by small

production batches and frequent change of grades and rolled profile, can be better handled by a semi-endless

concept. The latter is better suited to high-quality products, because casting speed can be optimized for the quality

to be achieved (with reference to bar center soundness and segregation in particular) rather than having to comply

with the requirements of the rolling mill.

Combining a billet welder with an induction heating system (and, if required, a gas-fired furnace), the combination

of gas- and electric heating can be optimized to fit the relative costs of gas and electricity; in addition, the formation

of scale can be minimized, and the feedstock temperature can be effectively controlled, eliminating differences

between head and tail. Consistent rolling conditions improve product quality, both in terms of size tolerances and of

mechanical properties.

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For plants focused on commercial grades, the advantages of endless rolling versus conventional rolling add up to a

considerable improvement of mill efficiency (utilization) and therefore to lower operational cost:

- Reduced energy consumption for billet heating

- 7-8% higher productivity due to the elimination of inter-billet gap time

- Material yield increased by 1.5 – 2 percent points

- Unplanned production delays effectively halved, as most interruptions of operational nature in

conventional rolling are related to the bar head

Energy consumption

Newly developed high-speed casting technologies result in higher temperature as the billets proceed from caster to

rolling mill. Surface temperatures of 850°C are normally achieved with semi-endless rolling. In endless rolling,

casting speeds in excess of 6 m/min ensure billet surface temperature around 950°C, so that only a surface-core

temperature equalization is needed before rolling.

The energy savings and associated savings of natural gas result into an opex reduction between 5 and 11 USD/t

compared to conventional minimills.

Yield

Considering the major material losses in a typical facility for long products, composed of a billet caster and a rolling

mill, we can identify the savings potential as follows:

- For continuous casting, state-of-the art operation with long casting sequences effectively minimizes the

losses related to head- and tail crops and tundish skulls; losses associated to scale formation and oxy-cuts

are negligible compared to the former.

- In the rolling mill, endless rolling offers high potential of increased yield (crop- and short-length related

losses practically disappear). The same savings can be achieved either with an endless- or with a semi-

endless process.

- Replacing gas-fired reheating furnaces with flexible induction heaters reduces the scale loss considerably,

contributing to the favorable yield of these plants.

- Last, endless or semi-endless process reduces the frequency of cobbles in the rolling mill, with favourable

effects not only on the yield but also on production efficiency.

For a typical 450.000 t/y facility the potential savings are obvious, as the losses can effectively be halved:

Yield and Consequences Conventional Endless rolling

Scale Build-Up 0.8% 0,3%

Head/ Tail cuts of billets 0.4-1,2% 0,2%

Short bars 0.8-1.2% 0.3%

Cobbles 0.4-1.4% 0.2%

Welding (if present) - 0.2-0.3%

Total Loss: 2.4-4.6%

(typical 3.5%)

1.0%-1.3%

Final Product: 450.000 mt tons Tons

Billet required to produce 450ktpy: 461,000-

471,700

454,000 – 455,500

Potential savings of billets: 0 7,000 – 16,700

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MINIMILL OPTIMIZATION BY DIGITIZATION

The progressive digitization and new technologies enable steel producers to achieve further improvement of quality

and efficiency by intelligent interconnection of automation systems of different levels, smart sensors, robotics,

advanced plant technology packages and maintenance systems:

- Automation solutions improve productivity, operator safety and availability of the plant. This comprises

automated procedures like scrap charging to the EAF and automatic ladle handling, as well as process

control through modern measuring and analyzing devices.

- Automated equipment supervision and process models allow prediction of possible failures of critical plant

components and lead to a reliable preventive maintenance system.

- Level 1 and Level 2 systems allow to operate each process unit with the best efficiency at a maximum

degree of automation.

The novel development is the integration of all these systems into a coherent “Digital Landscape”, which

maximizes the asset’s return by constantly optimizing the production process.

The digital landscape of a modern Mini Mill

Figure 4: Digital architecture of a modern Mini Mill. Source: Primetals Technologies

In the following, this concept is illustrated by looking at some examples of different automation solutions for

minimills.

Automation, Smart Sensors, Robotics for Mini Mill

Automated procedures in steel plants help to optimize not only standard operating times, but also leads to higher

safety and reduced manpower. The following automation solutions are available today for modern and efficient

minimills.

Scrap yard automation:

The unique design of the Quantum EAF allows full automatization of the scrap- and raw material charging to the

furnace. In addition, solutions already exist for fully automated circulation of the scrap buckets.

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Figure 5: Quantum Furnace and Automated Scrap Yard

Robotic applications

For EAF:

- Temperature Measurement and Sampling

- Tap hole Cleaning and Opening

- Tap hole Sand Filling

- Slag Door cleaning

- Ladle Tracking and Handling

For CCM:

- Shroud operation

- Temperature Measurement and Sampling

- Oxygen, Hydrogen Measurement

For Rolling Mill

- Robotized replacement of rolls

- Robotic Laying Head

Today’s standard for the above-mentioned operations are semi-automatic manipulators, designed for the specific

purpose. The disadvantage of such manipulators is that they need manual operation for attaching and detaching the

probes, meaning that personnel has to enter hazardous areas.

For some of the above mentioned operations, robotic solutions become more and more popular. At first sight robots

have higher investment cost, however they also have significant advantages compared to the classical manipulators.

Robots are able to fully automatic pick up and deposit the necessary probes and tools and this is a tremendous safety

improvement - no personnel needs to enter dangerous areas anymore. In addition, robots are flexible in their

movements and a change of measuring position or adding additional functionality are easy to implement. A good

example of this is the application of robots for one of the most dangerous operation: ladle lancing and tap-hole

opening.

TB2

Wait Pos SC

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Figure 6: Typical layout for an EAF robotic application

Through-Process Optimization

Basis of the intelligent TPO solution is the Through-Process Quality Control (TPQC) system, which creates a

central database by receiving quality- and process data of all production units via both Level 1 and Level 2 systems,

as well as from all types of field sensors and equipment.

The purpose of the TPQC is to ensure the desired product properties and improve product quality, by monitoring all

quality-relevant process parameters at defined quality gates along the full production route.

The TPQC creates an information-rich genealogy of each individual product manufactured, and makes it possible to

project process data of all production steps onto the length of the product. This allows users of TPQC to track

quality issues in very little time and analyze them by reviewing process data of all relevant production steps, which

is key for fast troubleshooting and claim management.

To ensure continuous quality improvement , the TPQC system allows the implementation of freely editable rules,

which are used for the execution of conformance checks during production.

In case of deviations, TPQC supports operators and quality engineers with root-cause analyses and automatically

generated suggestions for corrective and compensational actions. Thanks to the system’s customizability, users can

implement and preserve their process- and product-oriented know-how by creating and implementing rules tailored

to individual steel groups or grades.

The integration of all processing units into one interconnected TPQC-based network also permits the creation of

“through-process” rules, which extend the corrective and compensational actions to the preceding and subsequent

productions steps.

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Figure 7: Overview of Through-Process Optimization modules of Primetals Technologies

TPKH=Trough-Process Know-How TPQC=Through-Process Quality Control

The centralized data collection enables the generation of key performance indicators (KPIs), which inform about

technical and business-related achievements, and illustrate what progress has been made. Possible targets are new

product-quality or process-efficiency levels, both related to individual processing steps or the entire production

chain (throughout the complete production process, hence the attribute “through-process”).

TPQC implements various types of graphical human-machine interfaces to support staff members from the Quality

and production departments, as well as top-management executives, in monitoring and benchmarking production

conditions with respect to specific targets that are in alignment with the KPIs.

Big data mining and machine learning techniques can be introduced into TPQC via an interface that enables the

direct and user-friendly transfer of data to commercial analytics platforms. Outside expertise can be obtained for

instance when quality or process issues arise. All acquired data is structured and bundled by the Genealogy

function, which makes it easy to handle even highly detailed inquiries about product properties.

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Figure 8: TPQC user interface, KPI Viewer

Maintenance solution for Mini Mill Plant

MAT (Maintenance Asset Technology) is a Computerized Maintenance Management System (CMMS), which

allows creation and management of maintenance orders, convenient graphical planning and scheduling of

maintenance activities, maintenance related document management, reporting and related dashboards, digital

checklist and automated triggering of maintenance activities based on external data sources like condition

monitoring systems and TPQC. The MAT system provides all the functionality to manage repair and maintenance

activities of a steel plant.

CONCLUSION

The main factor for success in steel long products is the cost of production, together with cost of transportation and

cost of asset.

Use of the latest technologies available makes possible to reduce conversion cost significantly. These technologies

are focused on energy savings and on the integration of process steps into a single, uninterrupted flow.

Technologies for scrap preheating from the EAF off-gas reduce EAF operating cost by 20%. At the same time,

endless rolling brings along a further 10% reduction of conversion cost. Minimills combining these technologies

have a considerable edge on competitors which rely on traditional production processes.

At the same time, the measures aiming at saving energy reduce the environmental footprint of minimills, reducing

CO2 emissions and contribute to preserving our environment.

The integration of innovative, through-process control- and optimization functions anticipates further steps into the

transformation of minimills into highly-automated, “smart” facilities, which are able to supply product of ever-

improving quality in the most economic way.