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  • Making steel more sustainable

New initiative targets process enhancements to reduce energy consumption and improve environmental performance.

Energy accounts for approximately one-third of the cost of a tonne of liquid steel. To reduce this figure and improve our environmental footprint, ArcelorMittal Flat Carbon Europe (FCE) has launched Energize – a project to identify new and existing process improvements which effectively reduce energy use and to implement them at all FCE mills. The goal is to reduce energy costs by 10% over the next four years.

Energize focuses on the consumption and optimisation of energy, and the reuse of energy rich gases (known as off gases) which are produced during the steelmaking process. Off gases can be used as a heat source, to produce electricity in our internal power plants, or can be sold to external energy providers.

The Energize project will also identify where energy losses occur in the production chain. For example, after it is discharged from the battery oven, coke is normally quenched using water and the energy it contains is lost as vapour. However, if a dry quenching process is used, the residual energy can be recovered and used to produce electricity.

During the project, each mill will also undertake its own programme to identify further areas for energy savings. Best practices, such as the case studies in this article, will be shared across mills.

Decreasing energy consumption reduces both production costs and CO2-equivalent (eq) emissions. The four case studies detailed in this article have reduced CO2-eq emissions by more than 500,000 tonnes/year. That equates to removing almost 180,000 medium-sized cars from the roads for a year. The positive effects of these best practices will be multiplied as they are shared across all our mills.

Gent recovers flue gases

In the blast furnace of ArcelorMittal Gent (Belgium), iron ore and coal (in the form of coke) are transformed into liquid pig iron. The pig iron contains 4.6% carbon, way above the 0.4% required for quality liquid steel. To remove the excess carbon, it is burnt with pure oxygen.

During the combustion process, a large amount of energy rich flue gases are produced. Previously these gases were burnt off at the top of a chimney. However, since July 2011, ArcelorMittal Gent has diverted the flue gases to a 90,000 m3 reservoir.

Around half of the saved gas is utilised within the mill, while the remainder is sent to a local electricity generator. ArcelorMittal Gent estimates that this will reduce the mill’s overall energy consumption by 3% and decrease CO2-eq emissions by 170,000 tonnes/year. Reusing the flue gases within the mill has resulted in a drop in energy consumption of 0.7 gigajoules (GJ) per tonne of steel. While the cost of building the system was just over €38 million, ArcelorMittal calculates that this investment will be recovered within two years.

Bremen recovers converter gas

ArcelorMittal Bremen (Germany) has implemented a €41 million project to recover energy, lower dust emissions and reduce nitrogen-oxide (NOx) emissions. The project saw the construction of a basic oxygen furnace (BOF) gas recovery facility and a convertor dedusting system.

The gas recovery facility will allow Bremen to reduce CO2-eq emissions by up to 270,000 tonnes per year. Around 80% of the recovered gas will be burnt in the walking beam furnaces of the hot strip mill, replacing the use of natural gas. The remaining recovered gas will be used in the mill’s power plant to generate electricity.

During renovations to implement the new systems, the burners of the walking beam furnaces were adapted to reduce NOx emissions by over 25%. In addition to lower dust emissions and the recovery of energy rich gases, this is the third green effect of this project.

Avilés increases scrap content

To increase scrap content in its steelmaking process, ArcelorMittal Avilés (Spain) is overhauling its scrap handling capabilities. Modifi cations are being made to the scrap handling yard, loading crane, transport wagons, the loading bucket and scrap control system.

The changes will ensure that an extra 10 to 15 tonnes of recycled steel can be added to every basic oxygen furnace (BOF) charge. This will enable the recycled content of the BOF to be increased to a maximum of 80 tonnes, or almost 30% per load. Annual CO2-eq emission savings are estimated to be around 59,000 tonnes.

Eisenhüttenstadt improves hot charging

At ArcelorMittal Eisenhüttenstadt (Germany), an ongoing project to improve the logistics of transporting slabs between the caster exit and the hot strip mill has been completed. Advanced tracking devices are now connected to the line to sense the location of the slabs. Together with new software, the system ensures the fresh slabs retain as much heat as possible. This reduces the need for heating in the hot strip mill.

The target is to transfer at least 25% of all slabs at a temperature higher than 800°C, and another 15% at a temperature above 400°C. Total energy savings are estimated at 160 terajoules/year and CO2-eq emissions will be reduced by 8,800 tonnes/year.

Source: Update client magazine - May 2012