Reusing the By-products of the Steel Industry

BlueScope Steel's operations have created a significant by-products industry, in line with the company's commitment to reusing materials rather than adding them to the waste stream. Around 360 kilograms of by-products are produced per tonne of crude steel. These by-products are produced in the different stages of the production process including:

the coal face
cokemaking
ironmaking
steelmaking

sinter plant
water treatment
and in rolling mills

During each of these phases, there is a conscious effort made to minimise waste and to utilise by-products efficiently. The table below shows some of the by-products and their uses:

PROCESS

PRIMARY PRODUCT

BY-PRODUCT

Coal mining	Coal	Methane
Coal washery	Clean coal	Coal wash middlings
Coke ovens	Coke	Coke ovens gas BTX Naphthalene Tar Ammonium Sulphate
Sinter plant	Sinter	Sinter fines
Blast furnace	Molten iron	Blast furnace slag Blast furnace gas Blast furnace dust Thickener slurry
Basic oxygen steelmaking	Molten steel	Steel furnace slag BOS dust Flue gas Slag rake/kish
Slab caster	Steel slabs	Tundish skulls Crop ends Mill scale
Rolling mills	Rolled steel	Steel offcuts Mill scale

Coal Face to Coke Ovens

Coal and coke production are not processes common to all integrated steelmakers. However, BlueScope Steel's Australian integrated steelworks does have its own cokemaking facilities.

The modern, integrated steelworks depends on coal as a source of carbon for chemical reduction of iron ore, and as a primary source of energy. Various marketable by-products become available as the coal is processed into coke. Using these fuel by-products of coal in the major steelmaking processes contributes significantly to limiting the cost of steel.

Methane -	Appin Colliery, located on the South Coast of NSW, produces high quality coking coal. A naturally occurring by-product of the mining process is methane gas.
	At Appin, methane is now being converted to electricity. Ninety-four one megawatt gas turbine engines have been installed and the electricity generated is sold into the NSW electricity grid to create power. The methane is drained from the coal seams before, during and after mining, with additional methane taken from exhaust ventilation air. This power is sufficient to service homes.
Coal middlings -	In order to minimise the level of ash that reaches the blast furnaces, coal is washed and then blended with coal from different coal seams. The small size, high ash coal content is separated from the main coal stream fed to the coke ovens, and is instead burnt in the boilers to generate steam and electricity or exported as part of an energy coal blend.
Coke ovens gas -	During the coking process, coke ovens are heated by gases recovered from operations further down the line. But the gas produced by the coke ovens is itself also captured, cooled, cleaned and recycled back into the system as energy for heating and electricity generation, replacing the need to purchase natural gas.

Of the energy required to run the steelworks, up to 40 per cent may be provided by coke ovens gas (and up to an additional 40 per cent by blast furnace gas). When the coke oven gas is cleaned, the process creates some valuable by-products that provide raw materials necessary for other industries:

Ammonium sulphate is a well-known fertiliser used in both broadacre farming and in nurseries. BlueScope Steel exports the ammonium sulphate produced at Port Kembla.
BTX (a liquid consisting of benzene toluene and xylene) goes to the Chemplex plant in Melbourne, where it is turned into styrene monomer. This is used for plastic products like telephone handsets and is a vital ingredient of styrene cups and beads.
Tar and naphthalene are used to manufacture pencil pitch, which in turn is used to manufacture electrodes for the aluminium refining industry, plastics, paints and wood preservatives.

Coal face to coke ovens

Water Treatment

A biological effluent plant, designed to treat waste water from the coke ovens, was constructed at Port Kembla in 1991.

Using bacteria which thrive on a diet of cyanide, ammonia and hydrocarbons, the 'bug plant' removes 99 percent of cyanide, 90 percent of ammonia, 99 percent of phenols and 99 percent of thiocyanate found in the waste water. The bacteria are contained in tanks into which the water is pumped. Oxygen, phosphorus, lime and sulphuric acid are added. When the wastes are broken down by the bacteria, they are removed as a sludge that is squeezed dry and recycled to the coke ovens.

The remaining water is filtered before being recycled or discharged safely.

Sinter Plant

Iron ore contains a high percentage of very fine material which is unsuitable for feeding directly into the blast furnace. In order to make use of this product, it is first agglomerated by mixing with fine lime and coke. It is then passed through a flame chamber where it 'sinters' (or fuses) together. The sinter plant is also used to recycle other iron or lime dusts generated by other processes. Recycling by-products through the sinter plant is one way of recovering some of the fines produced in other parts of the steelmaking process.

Ironmaking

Slag is the basis for a multi-million dollar industry in Australia, and is a major by-products success story.

BlueScope Steel's Port Kembla Steelworks generates slag from two sources - blast furnace slag and steelmaking slag. Slag flows from the iron and steel furnaces as a molten mixture of limestone and the earthy components of iron ore coke that have separated from the molten iron and steel in the furnace.

It is then processed in two forms:

Rock slag -

is produced by allowing the molten material to cool slowly and solidify. It is then crushed, making it suitable for road base and aggregate.

Granulated slag -

is produced by the instant quenching of molten slag. The result is a sand-like product that can be ground and used as a cement replacement in the concrete industry. In this application, it is favoured for its durability, particularly in marine environments. It can also be used as a sand substitute.

Slag in this form has been used in projects such as the Sydney Harbour Tunnel, the third runway at Sydney Airport, the North West Shelf project, in the sea wall of the Sydney Opera House forecourt, and as road paving for sections of Sydney's F4 Freeway (because of its anti-skid attributes).

More recently, it has been used in the construction of the concrete walls, floors, columns and beams in many of the Sydney 2000 Olympic Games venues, including the Equestrian Centre and Velodrome.

Blast furnace gas and dust -

Gas from the blast furnaces is sent into a gas cleaning plant where dust and fumes are removed. The cleaned gas is reused as fuel and the dry dust fed back to the sinter plant.

In addition to coke ovens gas, a major part of the steelworks energy requirement is fuelled by the cleaned blast furnace gas. The remaining slurry, which contains zinc content too high to directly recycle, is put into a settling tank. Water is pressed out of the slurry, cleaned and put back into the harbour. The remaining fraction is stockpiled.

BlueScope Steel is looking at a process to economically retrieve the zinc and iron units.

Steelmaking

Steel furnace slag -	Slag from the basic oxygen steel (BOS) furnace has the metals removed and recycled back into the steelmaking process. This slag is used in road pavement, bottom ballast and aggregate in asphaltic concrete, and as landfill.
BOS dust -	This is removed from the exhaust gas of the BOS process in a slurry (or wet) form. It is mixed with the blast furnace slurry and treated the same way.
Flue gas -	It is not economically viable to recycle gas from the BOS furnace, so the gas is cleaned and then flared.
Slag rake/kish -	Fine graphite flakes are freed in small amounts from the slag-raking of ladles at the BOS. This material is not currently recycled.
Caster scale -	The continuous slab casting process produces caster scale, a fine iron oxide that flakes off the surface of steel. This is recycled back into the process by routes such as the sinter plant as a source of iron units. It is also useful in exothermic powders.

Rolling and Tin Mills

Mill scale -	Mill scale is a by-product of the rolling process, and is recycled in a similar fashion to caster scale.
Pickle liquor -	Pickle liquor is an hydrochloric or sulphuric acid solution used to clean strip steel after it has been rolled.

These solutions have been used by manufacturers of wire to clean the surface of rod and wire prior to wiredrawing or metal coating operations. In some mills, spent pickle liquor is passed through a recovery unit, returning the clean acid to the work baths, and generating a marketable ferrous sulphate product.

In 1992, BlueScope Steel joined with Orica and the NSW Water Board to convert some of this spent pickle liquor into a chemical that would greatly improve the quality of effluent from sewerage plants. It is used in sewerage treatment to break down detergents, washing powders and fertilisers that can otherwise cause excessive blue-green algae growth in the water system. The waste liquor (ferrous chloride) is converted to iron salts (ferric chloride) by Orica and is then used by the Water Board to bind and more easily remove solids from sewerage.

As part of the arrangement, BlueScope Steel uses hydrochloric acid at Packaging Products' tin mill pickle line, in Port Kembla. Using hydrochloric acid also provides the by-product of caustic soda, which can be marketed to displace imported caustic soda. Spent pickle liquor is also used at the Royal Australian Mint in Canberra, where it reduces the chromium (used to manufacture and clean coins) in waste water.

BlueScope Steel's Western Port Works in Victoria, Australia, converts most of its pickle liquor to hydrochloric acid at a regeneration plant. Here ferric oxide and hydrogen chloride gas are chemically produced and separated. The latter is absorbed in the rinse water from the pickle line and returned to the pickle line. Ferric oxide powder is sold for use in a variety of industries, including for the manufacture of audio and visual tapes and electric motor cores.

The Future

A number of other uses for by-products are in planning, or still in their infancy.

These include:

Coal wash -	Coal wash is the dirt and shale washed out of coal before it is sent to the coke ovens. It is currently used as landfill and as an ingredient in the BlueScope Steel soil substitute. Other potential uses are being investigated, including application as a construction material.
Oils -	Increasingly stringent requirements on the disposal of wastes to landfill has prompted a search for suitable treatment options.

In the past, BlueScope Steel has used a process in which waste oily sludges removed from steel rolling mill coolants are treated biologically to produce a product that can be successfully incorporated in soil mixes, and also enable the coolant to be recycled. The solids in the coolant are removed by centrifuge and magnetic separations. The resulting waste sludge contains high levels of tallow and mineral oils, solids and water. By mixing the sludge with granulated slag in a bioreactor, the oil and grease content can be reduced to the extent that the resulting material has a soil-like consistency. It can then be used as a component of the substitute soil mix.

The tallow oil purchased by BlueScope Steel for use as a rolling lubricant is itself a recycled product of the fast food industry - cooking oil. Recycled oil is also returned to the plant through the coal preparation area, where it is added in the coal grinding process at the hammer mill as a means of increasing the bulk density of coal charged into coke ovens.

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