Energy Use in BlueScope Steel's Steelmaking

Sources of Energy | Energy Reduction | Improving Technology | Improved Work Practices | The Future

Energy is an essential element of every facet of steelmaking, from the reduction of iron ore to molten iron, through the various stages of processing and finishing. The main sources of energy in steelmaking are coal, electricity, natural gas and by-product gas from coke ovens and blast furnaces.

At our Australian steelworks, energy makes up around 17 percent of the operating costs. Yet through improved technologies and practices, both energy use and greenhouse emissions in the Australian steel industry have progressively reduced over the last 20 years.

Since 1978, overall energy required to produce a tonne of slab through integrated steelmaking has been reduced by around 28 per cent. International Iron and Steel Institute (IISI) research shows that the amount of energy required to produce a tonne of steel is less than half of what it was 35 years ago.

Sources of Energy

One of the key raw materials in steelmaking is coal. It is used as a reductant (to convert iron oxide into metallic iron), as a carbon source to produce heat, and in the blast furnace to support the 'burden' (preventing the iron ore and fluxes from collapsing into the liquid iron, and providing a porous medium through which gases can pass.)

Approximately 90 percent of the energy required by the steel plant is coal-based - either coke, coke oven gas or blast furnace gas. BOS off gas (OG), a by-product of the process of converting iron into steel, is not collected at any of the BlueScope Steel sites. Refer figure below.

DISTRIBUTION OF TOTAL ENERGY

Energy Reduction

There are three main categories of energy usage in the iron and steelmaking process - and we continually seeks opportunities to reduce usage in each category.

The three categories are:

Energy supply - the supply and preparation of raw materials.
Energy conversion - processes for converting raw materials to liquid metal.
Energy consumption - processes which only consume energy. These include reheating and rolling steel, and the supply of services to ancillary processes. One of the larger consumers in this category is the boiler house, which produces steam for use in turbines to provide compressed air, process air (wind) to blast furnaces, process steam to process departments, and - if excess coke ovens and blast furnace gas is available - to generate electricity in-house.

The model below is based on BlueScope Steel's integrated steelworks at Port Kembla, New South Wales, Australia. It shows the distribution of energy sources for a modern steel plant.

Energy Schematic for a Modern Integrated Steel Plant

Improving Technology

Our drive in recent years to modernise our plant and equipment has resulted in improved environmental performance, raw material usage and energy efficiency. One example is the introduction of 100 per cent continuous casting in the integrated steelmaking process.

Continuous casting technology provides not only improved yields, but also significant savings in energy. It involves the casting of molten steel directly into slabs, blooms or billets, eliminating the need for ingot manufacture. Continuous casting replaces three far less efficient process operations.

These are:

Direct metal foundry - where ingot moulds are made.
Soaking pits - where steel ingots are placed to be reheated to a temperature suitable for rolling.
Slab mill or bloom mill - where ingots are rolled into semi-finished products.

At our Port Kembla Steelworks, the continuous casting process saves around 25 percent of the energy formerly used in making a tonne of slab steel by the ingot process. The resource energy required to extract and refine iron ore in the ground to produce steel is approximately 26 gigajoules/tonne.

This so-called 'virgin' steel is usually produced by the blast furnace-basic oxygen steelmaking route in an integrated steelworks.

At the end of a steel product's life, most steel is recycled as scrap, which consumes only 7 gigajoules/tonne (and has other environmental savings). This lower energy consumption is due to the high embodied energy of scrap, a legacy of the integrated process, and is the basis for the high economic value of scrap and high recycling rates.

Most scrap is reprocessed using electric arc furnaces, which are more suited to higher scrap charging rates and distributed, smaller scale production than the integrated process.

Although, steel is 100 percent recyclable, growth in demand (especially from developing nations) means there is a continual requirement for virgin iron ore production. Some virgin iron units are also used to produce many higher grade steels, and provide a sweetener for lower grade - or contaminated - scraps.

Our Australian integrated steelmaking operation is largely energy self-sufficient. Approximately 90 percent of the energy used is coal-based - ie. either coke, coke ovens gas and blast furnace gas.

Improved Work Practices

Apart from new technologies, better work practices have also contributed to greater energy efficiency in the production of steel. These include:

Audits
At our Port Kembla steel operations, energy audits have been carried out to determine ways to further reduce energy usage. These have resulted in savings of millions of dollars.

Modelling
Off-line energy models have been developed at some steel plants to evaluate the performance of existing processes under various operating scenarios, and to evaluate new processes.

These computer models monitor the energy flows within the plant, providing information on the cost efficient allocation of fuels, and helping to maximise the use of indigenous fuels, ie. coke ovens gas and blast furnace gas.

Research and Development
The development of lighter, stronger steels means less material is needed to do a specific job. This results in overall energy reduction because a greater number of products can be made from each tonne of steel, and the energy cost of transporting each product is reduced. For instance, roofing products and house frames are now made of high strength 500 MPa steel instead of 250 - 300 MPa steel. (MPa is a unit measure of strength.) Equally, the use of thinner and higher strength steels in the automotive industry has helped improve the fuel consumption of cars.

Most of the energy in steelmaking is consumed in the ironmaking stage of the process. There are practical limits and economic constraints on the extent and rate of change that can be undertaken in the steel industry at the present time, but these processes are continuously being evaluated.

Alternative iron making processes are being evaluated around the world, and the results of trials are being closely monitored and adopted as technology becomes viable.

The Future

The environmental issues associated with energy supply and use are many and, in some cases, complex. Overall, there are two basic ways in which these impacts can be reduced:

Changing the technologies we use; and/or
Changing our demand for energy.

Our continuing focus will include the pursuit of economically viable energy efficient processes; further investment in new technologies which economically reduce energy consumption; and energy modelling of processes to look for further improvement opportunities.

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