Firing up the old with the new: Preparing refractories for the future

By Liz Gyekye
Published: Wednesday, 26 August 2015

A strong US dollar, China’s economic slowdown and environmental issues are just some of the challenges that today’s refractories producers are having to contend with. Liz Gyekye, Chief Reporter, looks at what companies in the sector are doing to stay ahead of the game.

The steel and refractories industries go hand in hand, as the steel sector is the main consumer of refractories and an important driver of innovation. Around 60-70% of the world’s refractories go into steel making, while the rest are mostly used in the manufacturing of iron, cement, glass and non-ferrous metals.

Refractories, made up of minerals such as alumina, bauxite, chromite, dolomite and silicon carbide, are essential in the steel production process and can resist ultra-high temperatures of more than 1,500°C. They solve many problems relating to containment involved in the metal’s manufacturing process, which include contact with corrosive solids, melts and gases at high temperatures. 

These challenges are addressed through the use of refractory materials as linings to furnaces, kilns, flues, reaction vessels and ladles. The growth of the refractories sector is driven by a variety of issues, including economic progress in developing countries, an increase in demand for end products made in refractory-lined furnaces and growth in crude steel production. Therefore, when considering the future challenges and trends for refractories, it is important to look at crude steel production first.

Crude steel production in 2014

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Source: worldsteel

Steel doldrums

During the years 1950-1955, average global crude steel production rates per annum were 7.4%, according to the World Steel Association (worldsteel).  From 2000-2005, this figure stood at 6.2%, driven largely by growth in China. The corresponding statistic for the period of 2010-2014 stands at just 3.8%. This last figure demonstrates that the steel industry is no longer enjoying the levels of growth it experienced a decade ago.

This is due to a number of factors, succinctly summarised by the International Monetary Fund (IMF), which recently cut its forecast for global economic growth in 2015 from 3.5% to 3.3%. The reduction relates to a lower than expected economic performance from North America in the first half of the year, due to the strengthening US dollar, the Greek debt crisis, a subdued construction sector in China and recent Chinese economic troubles. This is bad news, when one considers that China represents around 49% of the global market for crude steel production, followed by Japan at 6.6% and then the US, India and South Korea.

Refractories manufacturing capacity, which built up to serve the steel market during the high growth years, is now feeling the pinch from the slowdown in steel output.

Other refractories producers, such as Austria-headquartered RHI AG, are also focusing their economic arguments on China. The firm says that Chinese steel imports have increased by 100% in the first half of this year, leading to overcapacity in the market and contributing towards high levels of competition in the refractories industry."Due to the general decline of steelmaking in the world and particularly in China, we can see overproduction in the refractories industry now," Sergei Odegov, CEO of Russia-based Magnezit Group, told IM. "At the moment, not only big, but also medium and small Chinese refractories companies are starting to enter foreign markets and offer very low prices for products and raw materials. So, only local companies with their own raw materials, or companies with product know-how, will continue to operate [successfully] in the market."

On the flipside of this argument, Marco Tonidandel, business development manager of Slovenia-based Seven Refractories, maintains: "On one side, we see Chinese sources reducing their output of high grade refractories because of scarce availability and mine exhausting. This is particularly true for bauxite. But on the other side, there are regulation changes, like the [lifting of the] anti-dumping fee on Chinese silicon carbide, opening access to Chinese raw materials in Europe to some extent. We have established a very reliable and flexible supplier base in Europe and probably those changes affect us much less than spot market-oriented refractories players."

Table 1: Major steel exporting countries in 2014

Rank

Total Exports

Million tonnes

1

China

92.9

2

Japan

41.3

3

European Union (28)

37.1

4

South Korea

31.9

5

Russia

27.0

6

Germany

24.8

Source: worldsteel

Another important ongoing trend for the refractories industry worldwide is the decreasing specific refractory consumption per unit of steel produced. The development and improvement of steel producing technology in combination with much higher process demands on refractory linings have resulted in a constant reduction of specific refractory consumption, from about 50kg/tonne in the 1960s to around 8-10kg/tonne today for modern steel manufacturing, according to Almatis’ global technical director of refractories, Andreas Buhr.

"Even in challenged steel markets, the trend towards better performing refractories suitable for the production of high quality steel products is ongoing," Buhr told IM. "Therefore, new business opportunities exist for speciality alumina raw materials."

Steelmaking technology changes have led to new requirements for refractories. Today, steel companies are aware of energy losses and the cost saving made possible by better refractory lining concepts – issues that nobody was concerned about 20 years ago. Examples of these steel technology movements are basic oxygen furnaces (BOF) replacing open hearth furnaces, the introduction of continuous casting and the growth of secondary metallurgy performed in steel ladles, helped by an increased appetite for low impurity steel from the automobile sector, according to Buhr.

High purity alumina for high quality steel

Extended processing of liquid steel in secondary metallurgy requires continuous adjustment and improvement of refractory linings and can be considered among the most important drivers for refractory innovations, Buhr says. It can only be performed with specific high-performance refractory linings, such as high purity alumina (HPA) refractories. These refractories must be thermodynamically stable in contact with steel, in order to avoid re-oxidation of steel.

Bricks are either high-fired carbon free bricks or carbon bonded spinel forming AluMagCarbon (AMC) bricks. Buhr explains that alumina-based carbon free refractories provide two advantages for the ladle side wall when compared to magnesia-carbon (MgO/C) bricks with carbon contents of 10% or higher. They avoid a carbon pick up of ultra-low carbon steels from refractory lining and have lower thermal conductivity – for example, 3.5 versus around 10 watts per metre kelvin (W/mK). Refractories for steel ladle side walls must withstand slag attack by aggressive, metallurgical reactive slag – for example, calcium-aluminate slag (CaO/Al2O3). Silica-containing high alumina refractories, such as andalusite or bauxite, show high wear-rates with aggressive, low-melting CaO/Al2O3 slag, explains Buhr.  Therefore, there has been trend towards HPA spinel refractories replacing andalusite and bauxite in ladle linings. High purity spinel refractories come in the form of either castables or bricks.

Table 2: Non-metallic mineral product US refractory market ('000 tonnes)

Item

2004

2009

2014

2019

2024

Non-metallic mineral refractory market

420

275

310

338

351

Ceramic products

205 

120

140

149

152

Glass products

70

55

60

62

64

Cement, lime and mineral products

145

100

110

127

135

$/tonne

940

1275

1575

1895

2210

Non-metallic mineral refractory market (mil $)

395

350

489

640

775

Source: The Freedonia Group

New refractories for steel ladles have also recently been unveiled by Brazilian refractories producer, Togni S/A Materiais Refratarios. The firm launched a new product, made from silicon carbide carbon, for use in torpedo ladles, which transfer melted iron from blast furnaces to steel shop areas. The company’s vice president, Livio Togni, says that the products have helped "the average life for a certain steel shop in Brazil to jump from 500,000 tonnes to more than 1m tonnes of melted iron". Togni confidently asserts that this is a "new benchmark in the market".

There has also been a drive by companies to improve optimal performance and maintain high levels of consistency, an achievement claimed by Alteo – a leading supplier of speciality alumina products to the global refractories and ceramics industries. 

"Both these trends reflect the pressure from users for longer refractory life," says Alteo’s director of marketing, Mike Rodgers. "The key example being the ever declining weight of refractory used per tonne of steel. Particularly pronounced in China, the speed of this shift towards quality raw materials is having a profound influence on Alteo’s products and organisational direction. We also sense that India could become the 'new China’, in terms of growth potential."

According to a report published by market consultancy group, TechNavio, last year, the refractories market in India is forecast to grow at a compound annual growth rate (CAGR) of 9.85% over the period 2013-2018. K Srinivasan, managing director of Indian refractories producer Carborundum Universal Ltd (CUMI), says that "70% of production is still going to steel and that remains the biggest market. This will not go away in a hurry. Steel on its own is very, very big. We have to be mindful of the fact that the industrial minerals sector as a whole has to work on something that has to be the next big thing for the steel industry. We can bring these niche materials into market and they do tend to get absorbed into high value refractories more quickly."

"So-called Indian refractories have mainly been taken over by European companies, such as RHI, Saint Gobain or [Japan’s] Krosaki in recent years. They are now all part of global corporations."

Srinivasan says that China is using recycled scrap more to produce its steel, so the country’s reliance on iron ore is declining. "That changes the kind of refractories they will use and the type of steel making that they will do – probably moving towards smaller furnaces. I think we will see disruptions; I am pretty bullish about the new materials driving the next big change. [The technology] will be lighter, more energy efficient and cleaner."

Like India, Japan’s steel industry is also a large market for refractories. Japan-based Shinagawa Refractories Co. Ltd produces refractories primarily for the steel industry and 80% of its client base is from this sector. Heiki Miki, Shinagawa’s executive officer of overseas business for Americas and EMEO, says that Japan has a mature steel market and its steel producers make around 110m tpa of steel. He explains that the group’s local customer base is important to the firm, however, the company has plans to expand and seek growth opportunities outside of Japan, in Asia, Oceania and the US, with its own brand of long-life refractory bricks. "Traditional bricks typically live for 2,000 charges but we produce bricks that can last for around 3,000 charges," Miki told IM.

Shinagawa is developing new refractories, such as magnesia-carbon bricks, called "super-dense highly-durable multi-hole plug (MHP) tuyere bricks", to help "make the best refractories for these steel companies to help them stay ahead of the competition".

Development of more "attractive" products and high performance materials are key trends in the sector. In the long term, Magnezit’s Odegov believes that nanomaterials are the future. "Today, experts across the world are going in this direction," he says. "In Japan, for example, there is the Institute of Refractories, which develops and uses nanoadditives. And we understand that in five years or more, a real qualitative leap in the production of refractories will be possible, thanks to the use of nanocomponents – for example, nanooxides or carbon nanocomponents. Our specialists are already deep in this process and working in close connection with scientists from the Moscow Institute of Steel and Alloys, South Ural State University, Ural Institute of Metals and production companies, which manufacture nanocarbon materials."

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Building up: Many of the materials used in infrastructure,
such as iron and steel, are manufactured in furnaces
lined with refractory bricks. (Source: RHI)

Down under

The steel industry’s drive to cut costs has been noted by Australia-based commodity trader, Ferrochem Pty Ltd. The company’s director, John Svynos, says that steel production in Australia has shrunk over the last five years from 8m tpa to 2.4m tpa and that this sector could be "in jeopardy, given the cheaper imports available in Asia". Syvnos says this issue is contributing to the drive to make cost savings. He notes that the steel industry in Australia has been approving many refractory finished goods from China, which were originally produced in Australia.

"The production of refractory bricks has now stopped in Australia since last year, as they could not compete with the imported products from China," Svynos said. "Monolithic products are the only refractory products now produced here. We used to import in excess of 1,500 tpm [refractory products], but we are now importing 300 tpm."

"We are lucky to be associated with Refmin China and as such I also look after several key customers for export in places such as Indonesia, the US and Thailand. The growth from these countries is coming from their cement markets. This additional business helps keep us afloat."

Aluminium filling the void

With the steel sector remaining lethargic in certain regions, India’s Technology, Information, Forecasting and Assessment Council predicts that the aluminium sector will be the only one to show sustained increased percentage consumption of overall refractories production in the next 10 years. It is not entirely clear what proportion of the world’s refractories goes into the aluminium sector, although estimates suggest that the figure is around 1% – a total of approximately 100,000-200,000 tpa.

Refractories have many functions in the aluminium process and are used in everything from electrolysis cells to furnaces. Netherlands-based Gouda Refractories BV provides refractory lining products for equipment in the aluminium, petrochemical, waste incineration and steel sectors. Around 45% of its customers are from the aluminium sector, 55% from waste incineration and only 5% from steel. Traditional industrial minerals used for the aluminium process have barely changed, according to Gouda’s engineer, Marcel Franken. 

Most carbon baking furnaces are constructed from tongue and groove alumina-silicate bricks in two main qualities but in many shapes, Jarvis explains. These are either 65% alumina or 45% alumina, based on high purity raw materials pressed into dense shapes with minimum porosity and maximum strength in the form of creep resistance.When alumina, the raw material for aluminium smelting, is delivered into the primary smelters, it is added with cryolite to large, high capacity electrolytic cells with prebaked graphite cathodes and anodes incorporated into the linings, which are otherwise mainly brick and insulation, according to UK-based refractories specialist and consultant, David Jarvis. The cells then need to be baked in carbon in baking furnaces. 

Alumino silicate bricks are also used in aluminium melting and holding furnaces. In her academic paper entitled "Refractory considerations for aluminium melting and holding furnaces",  refractories expert, Ruth Engel, owner of US-based Refractory Consulting Services, says that there has been a recent trend globally to switch from bricks to monolithics, due to their availability and cost advantages.

This is because modern furnaces need to treat much greater quantities of molten aluminium and alloys more quickly and at significantly greater heat inputs in the case of melters, she says. These furnaces are frequently also tilting furnaces rather than the traditional static design and this puts much higher metallurgical and mechanical load on the furnaces in operation, according to Jarvis. 

Consequently, modern furnaces need to operate at higher loads and last much longer between major repairs. Monolithics are used to meet this demand, due to their ease of availability.

Nevertheless, Franken, disagrees with Engel and Jarvis and says that this trend is being reversed and aluminium producers are now going back to bricks because of the challenge of installing monolithics.

"Not everyone is using monolithics," Franken says. "There is a risk when you use monolithics as you need well-educated, skilled people to make these kinds of installations because it is not easy to do. You also need to heat monolithics up slowly. If you heat them up too quickly, you get explosions."

Aluminium control

He concedes there are some good reasons to prefer monolithics, however. "The advantage of using monolithics is that they are simple to make. You have raw materials, you put this in a bag, mix it and there it is. In contrast, with bricks you need a delivery time of three months and you have to think in advance. A lot of people do not think in advance."

Several approaches are available to counter the ability of the aluminium in the process to wet and subsequently penetrate and interact with the refractory, Engel maintains. The use of anti-wetting additions to refractories in contact with molten aluminium is a common approach, especially for calcium aluminate-containing monolithics. 

Additives commonly used include barium sulphate and different types of fluorides, like aluminium fluoride (AIF3) and calcium fluoride (CaF2). Another approach is to add a phosphate, as this imparts highly non-wetting properties to the refractory and does not decompose until temperatures reach >1,500°C, Engel says. In bricks, the additives are incorporated into the mix prior to firing; in monolithics it can be the bonding agent. In addition, she says that the use of phosphate as a component of monolithics helps in bonding new and used refractories, which is particularly important when carrying out repair.

Franken concurs with Engel, maintaining that end users will increasingly look to extend the life of refractories and will need to add "special additives" in order to do so.  He says aluminium producers will need to use refractories that will also reduce downtime.

Franken notes that a lot of aluminium producers are putting new alloys in their aluminium. He explains: "In the old days, aluminium 

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Finished product: Only about 1% of the world’s refractories 
goes into the aluminium sector – a total of approximately 
100,000-200,000 tpa. (Source: George Esterich)

was 100% alumina. Just like steel was 100% iron ore. However, now you put in magnesia, zinc and all kinds of special additives to make aluminium.  This is due to a drive to improve the quality of aluminium or produce a special, thinner type of aluminium."

"So, if end users change this process, then your refractories will also need to be adapted. A lot of companies are saying 'we want to change the process, but we do not know what types of refractories can withstand this new process’. To a certain extent, a lot of firms are very conservative and do not want to change their refractories."

Franken points out that the aluminium industry accounts for only a small percentage of total refractories usage and in most companies, the focus tends to be much more on steel and cement. He says: "In the steel industry, you normally have one or two furnaces. In contrast, the aluminium industry has five or six. If one furnace is out of operation in the latter, this will not be a critical situation. However, in steel, if one furnace goes out, you lose 50-100% of your capacity."

"The steel maker is always a close neighbour to their refractories supplier. In contrast, with aluminium, there tends to be a distance between user and producer. Maintenance is also usually outsourced."

The use of refractories per tonne of aluminium will also go down in the future, in a similar trend to steel, due to process improvements and the increasing quality of refractory materials, he explains.

"You will never get to zero, because you will always need refractories but it will be less and less in the future. However, the products will become more expensive on one hand, but the costs for end users will go down on the other hand, because they will get more uses out of it," Franken adds.

Green refractories

As well as the drive for optimal performance, environmental challenges are also impacting refractories producers, especially ahead of the United Nations Conference on Climate Change – COP21 – in Paris in December. 

Industrial minerals giant Imerys has one of its many feet in the refractories business through its monolithic refractories subsidiary, Calderys. 

John Maxwell, vice president and general manager of Calderys, says: "Production of monolithic refractories leads to limited CO2 emissions because, contrary to refractory brick production, there is no heating nor drying in the manufacturing process."

Calderys has launched a company-wide initiative to increase usage of recycled raw materials. The scheme, which has intensified since 2011, reclaims materials from steel, aluminium and glass plants. "The materials are reclaimed, sorted, cleaned, dried and crushed to be re-used as raw material for Calderys’ products," says Maxwell. "For example, in Sweden, we reclaim 500 tpa of porcelain insulator production scrap from a local producer to manufacture refractory flooring tiles for the local steel plants."

Customers are also getting involved, Maxwell says. "They now save and sell back a large range of materials, such as bauxite and andalusite-based bricks. Some of the Calderys plants, like in Italy, are now equipped with crushing equipment allowing them to handle such materials."

The firm is also buying recycled raw materials to reduce its carbon footprint.  Ultimately, Maxwell says: "In order for refractory recycling to work, the European Commission and national governments must promote recycling as a means for the European Union refractories industry to become more competitive and sustainable."

It seems that most refractories producers with an eye on the future are pushing ahead improvements to their products and trying their best to jump, rather than dodge, macro-economic hurdles. As Joachim Paschke, director of business division in technical ceramics at Germany-based Nabaltec, concludes: "To be ahead of the game, you always have to adapt your material to meet the needs of your customers. This is an ongoing process and will never stop."

Use of chromite in refractories

There are two families of refractories that use chrome, one as chrome ore, also called chromite, and the other as chromic oxide. Magnesia-chrome (MgO>50%) or chrome-magnesia (Cr2O3>50%) refractories use chrome ore. 

According to the International Chromium Development Association (ICDA), refractory chromite consumption has decreased over the last 35 years, due to changes in steelmaking technology. Production of chromite as a refractory material is only 1% global chrome ore output, the ICDA states and according to industry sources, 100% of this is currently sourced from South Africa. However, it still has an important niche in the refractories industry. 

Mag-chrome refractories are used mainly in lead melting furnaces for battery recycling, some stainless steel production, in small argon-oxygen decarburisers (AOD’s), RH degassers. Incineration/gasifiers use chromic oxide bearing refractories. In this case, they are alumina-chrome with a very high chromic oxide content (>70%).

The ICDA states: "Cement and lime kilns are the second largest user of these refractories but only consume about 7% of world production. The use of mag-chrome bricks has virtually disappeared in cement kilns in Europe and North America, due to regulations and costs of disposal of the used bricks, which may contain hexavalent chromium as a result of the oxidising atmosphere in the kilns. In the rest of the world, the use of mag-chrome bricks is still widespread."

Source: International Chromium Development Association, industry sources