11th Global Slag Conference, Exhibition & Awards 2016
24 - 25 May 2016, London, UK
Reviewed by Dr Robert McCaffrey, Global Cement Magazine
Image gallery for the 10th Global Slag Conference 2016 (large gallery - may take time to load)
The 11th Global Slag Conference has successfully taken place in London, with 110 delegates from 24 countries in attendance. Sixteen presentations were given over two days, and the next Global Slag Conference will take place in Duesseldorf in May 2017.
Paul Mullins of Kallanish Commodities opened the 11th Global Slag Conference in London with an overview of trends in the global steel industry. Global steel production peaked in 2014 at 1.6bn tonnes, with Asia producing around 60% of the total: China produced 800Mt of this total. Japan, India, the USA, South Korea and Russia are also top producers. Demand is currently depressed in China, the USA, Russia and Brazil, but forecasts suggest that demand will increase through to 2017. Paul suggested that the ASEAN nations will see 5 - 7% per year growth over the next few years. China is still growing, officially at 6.5 - 7% per year, but steel demand is expected to fall by 3% in 2016 and 4% in 2017, due to the fact that the steel intensity of infrastructure development is falling. In addition, many cities around China have massive overstocks of housing supply, meaning that construction will slump, leading to further weakening in demand. Lower prices and weaker domestic demand has meant that a tide of Chinese steel has swept out of the country and onto the export markets. Beijing is now committed to reducing steel production capacity by up to 150Mt by 2020, although excess capacity is already currently estimated at 325 - 400Mt. A controlled stream of managed closures is not expected to impact the national economy, since much of the excess capacity is already effectively mothballed. Having said that, central edicts do not always work in China: "The mountains are high and the Emperor is far away," commented Paul. China's real aim it to build bigger, more efficient and less polluting steel production, not only to supply its own demands, but also to go out and conquer the rest of world. China is likely to export over 110Mt of steel each year, more steel than Japan produces overall. Paul suggested that NAFTA markets will be robust in the next couple of years, with construction enjoying low but steady growth. Falling oil prices have hit the Middle East, with both steel- and cement-intensive infrastructure weakening, but there has been a recovery in a number of other industries. Paul is extremely bullish on prospects for Iran. Trade and anti-dumping tariffs around the world have increased dramatically in the last few years, but end-user resentment means that there is also pressure against tariffs.
The second speaker at the conference, Charles Zeynel of ZAG International, started by saying that the 1.6bn tonnes of iron and steel production worldwide produces around 250Mt of slag. Charlie contrasted the outlook from the last Global Slag Conference in December 2014, when things were looking rosy in terms of both supply and demand, with the situation today. The fact is that the Chinese 'overhang' has depressed prices around the world and has led to widespread steel company losses. Demand for cementitious materials is still strong, even though cement demand growth has slowed to perhaps 1 - 2% per year. Charlie dated the moment of Chinese oversupply hitting the world markets to October 2015, causing the traded price of cement to drop by around $10/t to $40/t. Freight rates have dropped to incomprehensibly low levels, but a correction in shipbuilding is now taking place, so that the bottom is 'surely here.' Charlie concluded that the time of SCMs is here, including GBFS, flyash and FGD gypsum. The supply of blast furnace slag is actually reducing, as blast furnaces around the world are closed, and as the world converts to mini-mills and electric arc furnaces for smaller scale steel production and for steel recycling. The supply of GBFS is not expected to grow significantly: "There is not enough slag to go around and that's why cement companies have been busy locking in supplies over the last ten years." Japanese slag is of very high quality, but is now only available on allocation, and prices are rising. "I would not touch 95% of the slag that comes out of China, due to its variable quality, particularly from state-owned companies, while pricing policies can change practically from day to day," concluded Charlie Zeynel.
Sunghee Han, a senior manager at POSCO of South Korea, next gave an overview of slag markets in Korea. The country is the fifth largest steel producer in the world, with three integrated steelworks with a total of 71Mt of crude steel capacity, with the both the largest and second largest single-site steel plants in the world. Cement consumption is expected to decrease from current levels by about 10% by 2020, while GBFS supply is expected to increase due to increases in steel production. Housing construction is a major driver of cement demand, but this has been driven in the recent past by government policies rather than by market demand. In fact, 86% of Korean slag is granulated, with only 14% being air-cooled. A total of 13.9Mt of GBFS is produced in Korea each year, with 2.9% used for rice cultivation as a calcium silicate fertiliser, while the rest is used in the cement and concrete industry. There are four companies that are 'pure' GBFS players, that take the raw materials, grind it and then sell it on to cement companies. Grade I GBFS for use in concrete in Korea has Blaine of up to 8000, with lower grades ranging down to 4000 Blaine. POSCO expects a surplus of slag in the near future and is interested to find new applications for slag products. The climate of Korea presents challenges for slag use, being hot in the summer and very cold in the winter. The addition of activators to slag cement may improve early-strength gain and reduce cracking: Posment is an alkali-activator primarily made from a byproduct of the steel-making process that addresses these current weaknesses in slag-based cements. Posment is currently being used for concrete for the construction of high-rise towers in Korea.
The next speaker was Rajan Ramaswamy of OCL India, who gave an overview of slag supply and demand in India. The country produces 16Mt of slag each year, but does not currently use all of this material, the rest being either exports or 'sent to stockpile.' Rajan suggested that the Indian economy has a huge potential for growth. The Dalmia Bharat Group of which OCL is a part, is concentrated on the east coast of the country and has more than 25Mt of cement production capacity. The company has a target to reduce its clinker factor to a minimum through the use of flyash and slag. There is a trend towards the use of a higher proportion of LD and BOF slags.
Anil Parashar of Cem Consult next spoke about the growth of slag in the GCC region. The region is currently looking at an oversupply of around 30Mt of cement per year. The consumption of silica fume and flyash in the region has dropped, but GGBS consumption has grown. For example, the consumption of GBFS in the UAE has grown from just over 1Mt in 2012, to reach 3Mt in 2016, while the number of grinding plants has risen from 7 to 12. There are no blast furnaces in the GCC, so that all slag is imported. Japan has previously been the major source, but this is progressively changing over to Chinese slag. Regulatory changes are partly driving slag demand: The Dubai municipality has stipulated that concrete used in local infrastructure must contain significant quantities of SCMs. In addition, concrete with SCMs tends to have improved field performance in the countries of the GCC due to the challenging climate. Challenges to the increased use of slag in the GCC include the current design of grinding systems installed in the area, since grinding slag typically decreases the throughput rate of a mill previously used only for cement. Anil suggested that the addition of a roller grinder as a pre-grinding circuit can sufficiently increase capacity. At the same time, pre-drying of the slag may also be required, even in the GCC. The grinding capacity of the UAE is large enough to cater for the demand for the whole GCC, although there is currently a lack of adequate terminals for the material. There is also a trend towards the concept of 'captive production,' when ready-mixed producers own their own slag grinding units. Anil concluded that mega-projects like the Dubai Expo 2020 and the World Cup in Qatar will boost cement and slag demand in the GCC in the next few years.
In the second session of the conference, on slag and slag technology, Ian McDonald of Primetals Technologies Ltd spoke about dry slag granulation with waste heat recovery. Ian pointed out that each tonne of slag dumped for air-cooling represents 1.5GJ of wasted unrecovered energy, equal to around Euro3.5m for a 6000t/d furnace. Ian gave details of a process whereby molten slag falls onto a spinning cup and is spun out to impinge on a water-cooled receptacle wall: the granulated slag bed is then aerated, and the heated air can be used for heat recovery. The produced granulated slag has zero moisture, but due to its low porosity it has a low tendency to take onboard additional moisture, up to a maximum of around 2%. A pilot plant at the University of Leoben showed a glass content of 98%, with granules of 1 - 3mm, with particle size controlled by the speed of rotation of the spinning cup. An industrial-sized pilot plant is under construction at the VoestAlpineStahl Linz blast furnace, fed directly from a slag runner, and is expected to be commissioned in January 2017. The unit will finally accept full slag flow of 2t/min, with a maximum of 6t/minute.
Derek Schussele of Dust Control Technology, Inc. spoke about atomized mist dust-suppression for steel torching and slag generation plants. Spraying water onto dust sources increases its weight and cohesion and suppresses dust, but too much water can be destructive. Fine droplets sprayed into the air can entrap dust particles, and may be used with surfactants and foams to improve performance. Water droplets that are much larger than dust particles will tend to cause dust to pass around them in a slipstream effect, whereas the best dust capture will occur when the droplet size is the same as the dust size, such as atomised water droplets. Dust Boss offers a ducted fan solution that has a 'throw' of up to 100m with low water puddling. The cool down time of refractory bricks can be reduced with the use of a Dust Boss atomised water ducted fan.
Mark Tilley of Lixivia Inc. next told delegates about the use of stabilised BOF and ladle slag for use as fillers in cement. Lixivia's offering is the separation and purification of calcium from lime in slag using the 'Selex' closed-loop ion-exchange chemical leaching approach, which generates a more stable aggregate material, as well as producing valuable purified calcium products such as precipitated calcium carbonate, magnesium oxide and rare earths and at the same time sequestering carbon dioxide. The company is currently at the laboratory scale, but is preparing for a scale-up stage.
The final presentation of the day was given by Frank Dardemann of Loesche, who spoke about the mobilisation of hydraulically active phases in slag by producing ultra fine materials. Frank stated that the huge amounts of steel slag around the world are essentially unreactive. LD Linz-Donawitz slags are essentially the same as BOF slag, and the basis of the research was the realisation that there was a high proportion of potentially reactive mineral phases, principally belite, in the solidified slags. Frank gave details of an experiment where LD slags were ground at the Loesche research unit to high fineness, but he said that at the highest fineness beyond around 7000 Blaine that typical laser particle size determination becomes somewhat unreliable. It was found that the finer that the LD slag was ground, the closer the mix would come in 56-day strength to OPC mixes, despite having rather low early strengths. Heat of hydration of ultra-fine LD-based cement blends was lower than OPC blends, with peak exothermic reaction coming later than OPC. "The genesis of slag influences not only the chemical and mineralogical composition of the slag but also the grindability." Frank concluded that ultra fine grinding is extremely energy intensive, but that with further investigations, the optimum fineness and particle size distribution may be elucidated.
The Global Slag Awards Gala Dinner took place in the stunning surroundings of Stoke Park Country Club. The Global Slag 'product of the year' was awarded to Harsco Steelstop; Plant of the year went to Lafarge's Duquesne plant; the Global Slag 'innovation of the year' went to JFE Steel's rooler cooling of slag with waste heat recovery; the Global Slag equipment supplier of the year was Loesche; HeidelbergCement was awarded the Global Slag 'user of the year;' TMS International (the old Tube City IMS) was awarded the Global Slag 'producer of the year;' and finally, Ian Cottam of Cemex was awarded the coveted 'Global Slag Personality of Year.'
Luigi Cattini of the University of Leoben started the second day of the conference with a presentation on recycling of slag which is produced from the desulphurisation of pig iron. In Austria the land filling of any materials will soon b completely banned, so that it is imperative to recycle this problematic slag. The largest particles of the slag contain the largest amount of iron, which can be recovered, whereas the smallest particles of slag with low iron content and high sulphur tend to be sent to landfill. Through a series of experiments, Luigi and his research group discovered that the slag may be roasted in a rotary converter at high temperature (1400 - 1450C) to liberate sulphur, and with addition of calcium from lime the slag may then be reused in the blast furnace. The sulphur liberated is delivered to a sulphuric acid plant. The patents process is soon to be installed on a blast furnace at Linz, Austria.
Stefan Seemann of Humboldt Wedag next spoke about the use of high pressure grinding rolls (HPGR) for slag grinding. When slag particles pass through the gap between the grinding rolls many micro-cracks are created, which make the slag more grindable, reducing the energy requirement from 53kWh/t for grinding to 4000Blaine to as low as 13kWh/t slag. Stefan noted that the energy bonus increases with greater grinding fineness. The KHD Comflex circuit uses a Sepmaster third generation high-efficiency dynamic classifier, the HPGR roller press and beneath it a static V-separator. Stefan mentioned the world's largest slag grinding plant, with a capacity of 195t/h slag at 4500Blaine, built for a steel company in India, of which a pair was built for a total capacity of 390t/h. Energy consumption for the use of HPGRs is around 16 - 35kWh/t, depending on slag grindability and final product fineness. As a final case study Stefan gave details of the JUGPK Novotroizk cement plant in Russia which uses 30% blast furnace slag as a raw material source, which uses a HPGR for raw material grinding, leading to the world's lowest specific energy consumption for clinkerisation, of around 600kCal/kg.
The Global Slag conference featured a session on non-ferrous slags for the first time and Christoph Pichler of the University of Leoben started the session with a paper on the recycling potential of these important slags. Worldwide, total production of non-ferrous metals amount to the following: copper 23Mt (copper metals is worth approximately $4700/t; zinc 14Mt/t ($1900/t); lead 11Mt ($1700/t); aluminum 60Mt/y. All of these metals produce slags of various kinds during smelting and recycling. Christoph mentioned a number of research projects looking at recycling processes for zinc, lead and copper slags. As an example, Christoph mentioned the high content of zinc in filter dust from BOF and EAF which may then be treated in the Waelz furnace process: the slag generated form this process may then be further processed using reducing agents, either in solid cooled state or in a molten liquid state. Alternatively a new 2sDR process may be used to avoid the Waelz process, a two stage process involving pelletisation, clinkering (to liberate chlorine and fluorine), with the hot clinker n then immersed Ina hot metal bath. In another case the normal method of zinc production gives rise to large quantities of jarosite, potentially containing commercial quantities of lead, silver and rare metals. A special roasting step for sulphur is a prerequisite prior to a reducing process for the liberation of the commercial metals.
Next Gernot Roesler, also from the University of Leoben, spoke about utilisation possibilities for dumped lead slag. A huge amount of lead slag has been dumped over the last 150 years, derived from the lead blast furnace process, with the slag typically also containing zinc, silver, indium and germanium and gallium. Treatment options were often not applied, particularly 'in the early days,' even though the reducing processes are known to work well and are relatively easy to apply. Decontamination of dump sites means that the slag should now be reprocessed, with the valuable metals being separated and the inert residues becoming available for example for the construction industry. Around 1t of glassy slag is produced for each tonne of lead produced, with silicon, calcium and magnesium predominating in the slags, alongside lead, iron and other heavy metals. Hydrometallurgical processing seems to b inefficient since the zinc yield is too low, so that pyro metallurgical processing is preferred. Electrical slag cleaning furnaces, the top-blown rotary converter, the Waelz rotary kiln process or other (Ausment/IsaSmelt) technologies can be used for lead slag processing. Gernot suggest that the addition of lead slags to Electric Arc Furcnace Dust in the Waelz process may result in higher value 'Waelz oxide' byproducts from lead slag processing.
Nikolaos Katsiotis and co-authors from the University of Athens presented a life cycle assessment of OPC and blended cements with ferro-nickel electric arc furnace slag. Nikolaos referenced the lateritic nickel Laryma project of Greek company Larco, which has one of the highest costs of production in the world, which is a significant challenge in today's world of low commodity prices. Electric arc furnace slag from the ferro-nickel industry was previously widely used in the cement industry in Greece, despite its high chromium content of over 2%, but changes in European standards caused the practice to cease. A life cycle analysis suggests that the use of ferro-nickel slag at a rate of 5% reduces the CO2 emission from a tonne of Cem I 52.5 cement from 839kg/t to 797 - 827kg/t, depending on the classification of the slag as either a byproduct or as a waste and hence whether the environmental impact of the slag is 'carried' with the by-product or 'left behind' with the ferry-nickel process if the slag is considered as a waste.
Nick Jones of Harsco Metals and Minerals next asked (and answered) his own question, 'Is steel slag asphalt really that good?' Steel-slag-based asphalt lasts longer than natural aggregates, with less rutting, no stripping and less wear, with good skid resistance which is maintained throughout its service life, since it does not tend to take a polish like natural aggregates. The UK's Transport Research Laboratory undertook a study of Harsco's SteelPhalt steel-slag-based asphalt and found that the road surfaces did indeed perform better than equivalent natural aggregate asphalt surfaces. A new surfacing called Steelflow offers great potential for eve higher performance. The answer to Nick's own question seems to be an emphatic "Yes."
For the final presentation at the conference, Sebastian Teir of the VTT Tchnical Rsearch Centre of Finland spoke about the production of filler and coating materials in the form of ground synthetic and precipitated calcium carbonate from steel making slags. Pic is produced by calcining high quality lime won't,e adding lime with water and adding CO2 to precipitate the fine mineral. The Mina's are used as fillers and coatings for paper making and around 74Mt/ is used worldwide. Sebastian used an ammonium salt solution to extract around 50% of the calcium from a finely ground steel slag to produce a slurry, from which a calcium-rich solvent can be derived: the addition of CO2 leads to precipitation of calcium carbonate and as part of the process the ammonium solution is partially regenerated. A laboratory-scale pilot plant at the University of Aalto in Finaldn has been able to produce PCC of high purity and brightness with potential for use as a paper filler. Sebastian mentioned a techno-economic assessment case study for a pair of industrial facilities: The Tornio stainless steel plant in Finalnd produces 280,000t/y of argon oxygen decurburisation and ladle slag, while nearby the Veitsiluoto paper mill annually uses 60,000t of PCC. The Slag2PCC technology has shown that in this case there is only weak extraction of calcium from blast furnace and ladle slag, and the production of scalenohedral PCC was possible but expensive. However, it was possible to economically produce rhombohedral calcite and aragonite of a coarser size, which can then be ground to the required size. The process would be economic if the input cost of the slag into the process was zero, while it would be yet more profitable with a significant CO2 price, since the process acts as a carbon sink, reducing emissions by 0.3t CO2 per tonne of PCC produced. A residual slag byproduct with moisture content of around 10% is also produced,which also contains a remnant of the ammonium solvents. The slag residues could be used in concrete, for mine filling purposes and as a geopolymer. The UK company Carbon8 has produced artificial aggregates from AOD slag residues and this is a potential use for the slag residues from the current study. Briefly he mentioned that he has also been working on the use of slags as a raw material for the capture and sequestration of CO2.
At the end of the end of the conference, a number of prizes were presented at the farewell party. In the best presentation awards, Juha Koskinen of Tapojärvi Oy was given an 'honourable mention,' Christoph Pichler of the Montanuniversitaet Leoben was thrid, Ian McDonald of Primetals Technologies Ltd was second and the winner was Nick Jones of Harsco Metals and Minerals.
Delegates strongly commended the event for its convivial and collegiate atmosphere, and for its smooth and punctual organisation. Delegates were unanimous in the approval of the destination for the next, 12th, Global Slag Conference and Exhibition, and agreed to meet on 18-19 May 2017 in Düsseldorf, Germany.