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BEST AVAILABLE TECHNIQUES ON THE PRODUCTION OF IRON AND STEEL. Group 9. IRON AND STEEL INDUSTRY. This BREF covers the processes involved in the production of iron and steel in integrated steelworks. Iron and steel are important products that are widely used.
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Include both the technology used and the design, built, maintenance and operation installation.
Techniques developed in the relevant industrial sector, under economically and technically viable conditions.
Generally, two systems can be used to recover energy from the BOF gas:
Combustion of BOF gas in the converter gas duct and subsequent recovery of the sensible heat in a waste heat boiler.
Suppression of BOF gas combustion and storage of the BOF gas in a gasholder for subsequent use.
A high zinc content in the blast furnace has an adverse affect on correct operation. This zinc mainly originates from the scrap charged into the basic oxygen furnace. The release of Zn can fluctuate strongly from one cast to another. The same problem, but to a lesser extent, applies to lead (Pb) or cadmium (Cd).
Oxygen steelmaking is a batch process. In order to monitor progress samples are taken from the steel bath for analysis. It used to be necessary to interrupt oxygen blowing and tilt the BOF in order to take the sample. This was a time consuming process and it increased emissions from the BOF. In a modern plant samples are taken on-line during oxygen blowing by means of a sub-lance.
During oxygen blowing, BOF gas is generated.This gas is loaded with a large amount of particulate matter. The BOF gas is recovered for use as a fuel. Primary de-dusting is usually performed by venturi-type scrubbers (approximately 90% of the plants) or dry electrostatic precipitators. Prior to the venturi or the ESP, coarse particulates are usually removed by means of a deflector
Secondary off-gases result from following operations:
Reladling and deslagging of hot metal.
Tapping of liquid steel and slag from BOF (converters). Secondary metallurgy and tapping operations.
Handling of additives.
In most oxygen steelmaking plants, scrubbers are used to reduce emissions to air from the primary gas flow. This potentially transfers pollution from air to water so the wastewater generated is usually recycled and treated before discharge. The water from the scrubbers mainly contains suspended solids; Zinc and lead being the main heavy metals present.
The most relevant use of water considered here is the water used for the cooling of the elements of the furnace. Additionally, some water may be used for the cooling of waste gas or in the secondary metallurgy section.
The primary and secondary emissions to air are of high relevance. The available abatement techniques should be fed with the raw emissions as complete as possible. Thus the collection of the emissions is important. The combination of 4th hole (in case of three electrodes) respectively of 2nd hole (in case of one electrode) direct extraction with hood systems (or furnace enclosure) or total building evacuation are the most favorite systems.
Post combustion in the furnace is developed to use a maximum of chemical energy of the CO in the furnace and to improve the energy balance, but CO and H2 are never completely oxidised in the furnace; for this reason, it needs post combustion.
In order to reduce organic micropollutants in the total off gas (primary and secondary emissions), especially PCDD/F lignite coke powder can be dosed to the duct before the bag filters.
EAF slag can be regarded as an artificial rock, similar to natural rock, consisting of iron-oxides (FeO), lime (CaO), silicium-oxide (SiO2), and other oxides (MgO, Al2O3, MnO) EAF slags are characterised by high strength, good weathering resistance, and also high resistance against polishing. They also have properties, that make them suitable for use in hydraulic engineering.
There are two method of dust recycling:
The emissions of organochlorine compounds can be reduced by minimising the input with the scrap.
This compounds are contained in several technical devices like washing machines, hair driers, cooker hoods, fluorescent lamps…
In recent years new furnace types have been introduced that might be realised at industrial scale.