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View of long-life blow mould for use in blast furnace.
© BFI
Industry - blast furnace technology
11.04.2018

Springtail. The tiny arthropod is approx. four millimetres long.
© Technische Universität Dresden, Institut für Botanik

Surface structure of long-life blow mould with lotus effect.
© BFI

Coating prototype from the natural world: Electron microscopic imaging of hydrophobic and oleophobic skin surface of a springtail. The consistent hexagonal structure of the collembola cuticula is evident.
© Technische Universität Dresden, Institut für Botanik

Using bionic surfaces on blast furnace

In blast furnaces, air approx. 1,200 °C in temperature is blown into the reaction chamber for the reduction and melting process of iron. Special water-cooled nozzles made of copper are used for this, known as blow moulds. These are susceptible to damage or destruction by red-hot droplets of iron. This then costs time and money to put right. Researchers have now been able to design the surfaces of these blow moulds to allow liquid iron to simply drip off. This new beading effect is similar to the lotus effect seen on leaves.

The most common cause of blast furnace hold-ups are burnt-out blow moulds. These are usually damaged by the blow mould surface coming into contact with liquid iron ore running down.

To minimise such damage, the researchers looked at how they could develop a protective mechanism for the blow moulds, functioning along the lines of the lotus effect. An ambitious goal given the task involved: keeping not water droplets but liquid iron ore well away from the copper surface in blast furnaces. While the melting point of copper is 1,084 °C, the surface of the (expensively cooled) moulds in the blast furnace are exposed to temperatures of up to 2,300 °C. With the new surface texturing, the researchers expect the copper blow moulds to withstand the prevailing extreme temperatures in the blast furnace for longer. If liquid metal at temperatures of between 1,500 and 1,800 °C is prevented from lengthy, intensive contact with the mould, instead beading, the heat flow into the blow mould is drastically reduced and consequently the risk too of these being damaged or burnt through. The resulting lengthening of the service life of blast furnace blow moulds leads to a reduction in the unproductive use of energy, reduced CO2 emissions and lower operating costs.

The project “Boosting energy efficiency in blast furnace operation by increasing system availability using innovative long-life blow moulds”, which is funded by the German Federal Ministry for Economic Affairs and Energy, will conclude in the course of this year with field testing. The bionic surface structuring developed by the multidisciplinary research group, whose members include botanist Prof. Christoph Neinhuis and physicist Dr Wilfried Konrad of the Faculty of Biology of TU Dresden and Dr Jörg Adam from the VDEh Betriebsforschungsinstitut (BFI) together with Siegfried Konietzko from blow mould manufacturer Lebronze Alloys – Hundt & Weber, is already patent pending.

Air cushions protecting blow mould from liquid iron

For the new design of the surface, researchers looked to the skin structure of small ground-dwelling springtails (collembola). The body surface of these arthropods is extremely hydrophobic owing to a network of holes and depressions confining air. Acting as a thermally insulating layer, a similar air cushion protects the blow mould, the surface of which is designed based on this natural example. The necessary surface structure is straightforward to produce and is then chemically modified.

Complete and effective beading...

Dr Jörg Adam states: “We have already seen very good results in laboratory trials in the BFI. Liquid iron ore is shown to bead and roll off the surface of the conditioned test specimen - an effect is observed here in a high-temperature setting that compares to the lotus effect on plant leaves. We see considerable potential to use this effect for other metals and surfaces too.

Investigations performed to date have shown that an uncooled model plate measuring 30 to 35 mm thick, which otherwise would melt through in just a few seconds in contact with liquid iron, does not heat above 200 °C with the coating.

Refinement and preliminary testing have now advanced research to the stage of being able to perform practical testing on manufactured prototypes in a blast furnace. This practical testing is now in the preparation stage. Researchers will be looking at how the coating responds to the stresses experienced in operation.

Practitioners have shown great interest in using these more durable blow moulds. As they can be operated for longer before replacement becomes necessary, large volumes of energy can be saved; this is due to the fact that the full range of blast furnace peripheral equipment must continue running while blow moulds are replaced. The additional outlay in terms of coke that this entails equates on average to approx. 1,500 GJ per instance of downtime. Experts at the BFI expect energy losses in Germany due to blow mould damage to be reducible by around 1,600 TJ, calculated over a 12-month period.

For their efforts, the researchers were presented with the Materialica Gold Award in 2017 in the “Surface and Technology” area as part of the eMove 360 trade fair event in Munich.

(gh)

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Addresses

Project planning and coordination, laboratory, technical centre and industry trials
VDEh Betriebsforschungsinstitut GmbH

Effect of textured surfaces in high-temperature setting
TU Dresden, Institut für Botanik

Blow mould manufacture, technical centre and industry trials
lebronze alloys Germany GmbH - Hundt & Weber

Links

Learning from nature
Video by TU Dresden on the functional principle of liquid-repellent skin structures of springtails (in German)