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Big River Steel – the latest design of mini-millThe Big River Steel mini-mill being built on the banks of the Mississippi in Arkansas, USA was designed and supplied by SMS group and will contain the most sophisticated equipment yet installed in a mini-mill for the production of high-tech strip steels for a range of high-end markets – matching the capabilities of the traditional integrated route strip producers. Energy consumption and environmental performance will be class-leading.

With the building of this new steelworks, Big River Steel and SMS group intend to set new standards

for tomorrow’s steel production. What the name references, apart from its location on the banks of Ol’ Man River, is the massive flow of goods that is going to travel on the waterway to and from the plant. The $1.6bn project to produce 1.5Mt/yr of strip represents a step change for the US steel industry. By applying innovative, clean and energy efficient processes, the company will produce high quality steels for the energy, automotive, oil and gas industry from recycled steel scrap and contribute significantly to achieving President Obama’s ambitious climate protection goals. There are also plans to double this capacity in two subsequent expansion stages.

The groundbreaking ceremony took place in September 2014 and steel production will start in the first half of 2016.

TARGETING SUSTAINABLE STEEL PRODUCTIONThe International Energy Agency (IEA) expects the global consumption of electricity to double by 2030. This is the same time period covered by President Obama’s climate protection initiative, which aims for a 30% cut in US emissions of CO2, fine dust, nitrogen oxides and sulphur dioxide by 2030. As these regulations apply to steelworks as well as electricity utilities, new efficiency standards for vehicles and improved energy efficiency of household appliances, now is the ideal time to launch an innovative steelmaking plant and fully respond to the spirit of these climate requirements with particularly clean, energy-efficient steel production from regionally sourced steel scrap.

Additionally important, the range of quality grades produced here will be geared towards the higher performance demands of challenging, fast-growing niche markets, aided by its RH Top degasser and long CSP® tunnel furnace. Specifically, alongside standard steel grades for construction and white goods, there will be a focus on high-strength, multiphase steels for structural

Author: Thilo SagermannSMS group

STEELMAKING AND CASTING

automotive parts. The automotive industry is expected to require ever more lightweight, consumption-optimised, high-strength materials.

As well as the burgeoning e-mobility trend that is driving demand for small, safe and weight-optimised vehicles in the USA, the plant will also target new branches of industry that can offer crucial market advantages through the material properties of these high-performance steels. Ranking high on the product list will be high-quality pipe grades up to X70 for pipelines in oil and gas transportation, with an aim to advance the mill to also make X80 products.

The third key product group is electrical steels. These are enjoying rapidly growing demand as increasing energy consumption in the US requires ever better networks with correspondingly more powerful generators and transformers. These must adequately cope with grid fluctuations caused by irregular power feed-ins of renewable energy sources as well as cyclical consumption. Therefore, unlike other steelworks in the region, the plant is specifically designed with technology capable of the complicated production route of these types of silicon strip.

Big River Steel is also planning to produce steels in gauges and widths previously not yet available from mini-mills.

TRUST THAT HAS GROWN OVER DECADES The main initiator of the project, Chairman and CEO of Big River Steel, John D Correnti, is a pioneer in the future-oriented steel industry, and SMS group was chosen as the contractor as, for the last 30 years and more, Correnti and SMS have set new standards in steel production, as for example at Nucor, with the first Compact Strip Production (CSP®) thin slab technology plant involving casting the liquid steel into near-net shape thin slabs and combining the caster with the rolling mill via a tunnel furnace. At the time this process was revolutionary, but it is now globally established. a

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SMS is responsible for the metallurgical plants, rolling mills and coil logistics, as well as all the cold strip process lines, including batch annealing furnaces and all electrical and automation systems. All components will be tested and commissioned on the basis of the proven SMS Plug & Work method. The Düsseldorf consulting company MET/Con supported SMS group and were actively involved in the specifi cation and layout of the new steelworks. Big River Steel is the third largest order in SMS group’s corporate history.

PLANT FLEXIBILITY – A HALLMARKCore elements of the steelworks are a DC electric arc furnace, a double ladle furnace, an RH-Top plant for secondary metallurgy, a single-strand CSP® plant, a coupled pickling line/tandem cold mill and a hot-dip galvanising line. A plant schematic is shown in Figure 1. The key secondary metallurgy unit for high-quality steel production is the RH-Top degassing plant to be supplied by SMS Mevac for decarburisation as well removal of unwanted gases such as hydrogen and nitrogen (see Figure 2). A sophisticated process with a rapid-change system including pre-heating and vessel repair stand as well as a dedicated crane guarantees the required high productivity.

Downstream of this, there is a single-strand CSP® plant with roller heat furnace and a 6 stand CVC® Plus rolling

r Fig 1 Plant layout of the whole mini-mill complex

r Fig 2 RH-Top vacuum degassing plant

r Fig 3 Layout of CSP®

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mill with a design capacity of 1.5Mt/yr of hot rolled coils (see Figure 3). The capacity can be extended to 3Mt/yr with the addition of a second casting strand, also shown in the fi gure. The plant will cast and roll the widest thin slabs to date, measuring 1,930mm wide, so ensuring that the company meets the special requirements of ERW tubes.

WIDE PRODUCT RANGE FOR DEMANDING MARKETSOne-third of the hot rolled product passes through a continuous pickling line with a turbulence pickling section where the material is descaled and oiled ahead of sale as hot strip. The remaining two-thirds proceed directly from the pickling section to a tandem cold rolling mill where roughly 900,000t of the pickled hot strip will be rolled. Half of this rolled cold strip then travels to a continuous hot-dip galvanising line (also designed to also operate as an anneal-line only; see Figure 4). The other half of the rolled cold strip proceeds through a discontinuous route with a batch annealing furnace and off-line skin pass mill, emerging as carbon steel or high-quality electric steel (see Figure 5).

Big River Steel is the only mini-mill in the USA that boasts technology for such a wide range of cold rolled and fi nished products, giving it the capability to produce both semi-fi nished non-grain-oriented grades as well as the entire spectrum of laminated electric motor steels.

HOLISTIC PLANNING FOR SUSTAINABLE SUCCESSTo meet the high environmental requirements that apply here, Big River Steel will rely on state-of-the-art fi lter and water treatment systems in all its plants. This means, for instance, that the dusts in the gas purifi er will be collected and fi ltered, and by-products such as zinc dusts will be recycled in special reduction processes that recovers valuable raw materials. There will be NOx treatment in the universal annealing and hot-dip galvanising line that also helps reduce emissions to such an extent that the steelworks will be one of the cleanest in the USA.

The electrical and automation systems for all plants will be controlled in a process-spanning way by the SMS X-Pact® solution to provide optimum productivity and product quality. This includes a secure power supply for the steelworks, fully automated logistics systems, process monitoring and control from casting to cold rolling, drive control and sensors (Level 0), integrated production planning (Level 3), and all technological controls and process models (Level 1 and Level 2). MS

Thilo Sagermann is with SMS group, Düsseldorf, Germany.

CONTACT: communications@sms-group.com

r Fig 5 Layout of the universal annealing and galvanising line

r Fig 4 Layout of the pickling line and tandem cold mill