Highly Efficient Mini-Mills with Innovative Scrap Pre-Heating and Direct Rolling of Long Products

Transcription

1 Highly Efficient Mini-Mills with Innovative Scrap Pre-Heating and Direct Rolling of Long Products St. Fellner 1, C. Tercelli 1, J. Buttler 2 1 Primetals Technologies Austria GmbH Turmstraße 44, Linz, Austria, 4031 Phone: stefan.fellner@primetals.com 2 Primetals Technologies USA LLC 501 Technology Drive, Canonsburg, State, USA, Phone: 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 percentage points. Use of advanced automation technologies (smart sensors, robots, integrated process control and optimisation solutions) improves plant operation and utilization. (PT14 IN1E) Rev. 0 Page 1 of 11

2 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 years 1, 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 Countries 2 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. Studies 3 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 routes 4. 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 Jim O'Neill, Dominic Wilson, Roopa Purushothaman, Anna Stupnytska: How Solid are the BRICs?, Global Economics Paper No. 134, Goldman Sachs, 1. Dezember See World Steel Dynamics, Publication of AIST March 2014 and McKinsey&Company 3 rd Steel Scrap and Raw Material Conference, September 2017, Bangkok 4 Except for DR-based facilities for Long Products, predominantly in operation in Middle East (PT14 IN1E) Rev. 0 Page 2 of 11

3 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). 70% Conversion Cost Share from Scrap to Product 60% 50% 40% 30% 20% 10% 0% Melting Rolling Auxiliary Facilities Personnel 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 (PT14 IN1E) Rev. 0 Page 3 of 11

4 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 (PT14 IN1E) Rev. 0 Page 4 of 11

5 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$/kg kg/t 4.4 US$/t 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$/t Savings per ton US$/t +11% 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. (PT14 IN1E) Rev. 0 Page 5 of 11

6 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 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 semiendless 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 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 % 0.3% Cobbles % 0.2% Welding (if present) % Total Loss: % (typical 3.5%) 1.0%-1.3% Final Product: mt tons Tons Billet required to produce 450ktpy: 461, , , ,700 Potential savings of billets: 0 7,000 16,700 (PT14 IN1E) Rev. 0 Page 6 of 11

7 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. (PT14 IN1E) Rev. 0 Page 7 of 11

8 Wait Pos SC TB2 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. (PT14 IN1E) Rev. 0 Page 8 of 11

9 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. (PT14 IN1E) Rev. 0 Page 9 of 11

10 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. (PT14 IN1E) Rev. 0 Page 10 of 11

11 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 everimproving quality in the most economic way. (PT14 IN1E) Rev. 0 Page 11 of 11