12th Global Slag Conference, Exhibition & Awards 2017
18 - 19 May 2017, Düsseldorf, Germany
Image gallery for the 12th Global Slag Conference 2017 (large galery - it may take time to load)
The 12th Global Slag Conference 2017 has successfully taken place in Düsseldorf, Germany, attracting 130 delegates from 29 countries to listen to 19 presentations over two days, alongside an exhibition of slag-related services and equipment.
Charlie Zeynel of ZAG International started the conference with a stark statement: "Demand is exceeding supply: we are running out of slag. There is 'way too much' clinker production capacity in the world right now, and people ought to be thinking about building grinding stations rather than new clinker production capacity." Most of the iron and steel producers have sold out their slag and pricing has changed dramatically. The US cement market is now growing at '5-8%/year for the next ten or 15 years,' but freight rates have leapt from historic lows and are now once again a major factor in delivered costs, having increased by around 35% from 2016 to 2017. Imports into the US may be problematic in the coming years. Charlie pointed out that the question of the ownership of the slag is critical, since the owner has the power to decide on pricing and allocation. However, the ownership of the slag is not always clear. Blast furnaces are no longer being built, so that the supply of blast furnace slag will not increase. China dominates in this area, as in so many others: it produces 60% of the global total of pig iron each year and an equally large proportion of the global total of slag. Around 360Mt of blast furnace slag (BFS) is produced worldwide each year, with 75% of this being granulated to produce around 250Mt of granulated BFS. China produces 170Mt of this GBFS, Japan 30Mt and the rest of the world produces the remainder - 50Mt. Japan uses the majority of its own GBFS, with only around 10Mt made available for export. Slag product prices are inexorably moving upwards - that's if you can find the product to buy.
Michael Connolly of TMS International LLC next gave details of the status of slag and slag products in the USA. He pointed out that Mr Trump has told his administration to do what it can to 'oil the wheels' of industry, and has mandated his officials to repeal 75% of Federal regulations. However, it is the states that regulate non-hazardous materials including slag products. A number of states have recognised that slag is not a waste but is a product, provided that it is not discarded. Michael went through some of the regulations of the different states, pointing out that the use of slag products in some states require extremely onerous stipulations (for example in Illinois, where written notice is required to be given to adjacent landowners that industrial byproducts are being used in any project). In general, regulations vary wildly from state to state, from almost outright bans to widespread use. Through diligent advocacy work, US companies and other organisations - notably the National Slag Association - are gradually persuading regulators that slag products are 'a good idea.'
Christian Kohl of Kallanish Commodities next spoke about trends in steel supply. Christian pointed out that there has been a recovery in prices for steel products in the last 18 months, starting in spring 2016 and with a strong 'kick' in autumn 2016. He suggested that prices started to rise once some particular large buyers entered the market, causing a stampede, but steel prices were also backed by iron ore price increases. European efforts to stem a tide of imports of steel products from Asia also helped to boost steel prices in Europe, although these tariffs have not been universally popular with steel buyers. Global crude steel production was 1.6bnt in 2016, with China producing 800Mt - which, if true, is well beyond what was needed. The Chinese government now plans to reduce its capacity to a more sensible total of around 150Mt by 2020.
Tony Murray presented on behalf of Smithers Pira on key market trends for slag and non-ferrous slags, to 2027. Tony suggested the key trend will be that the global supply of BFS will reduce over the next decade due to the closure of Chinese blast furnaces.
Frank Dardemann of Loesche next introduced a new process for the production of cement clinker from steelmaking slag. Frank pointed out that other uses of slag have much lower value compared to using slag products to substitute for cement clinker, so that using steel slag as a supplementary cementitious material makes a lot of sense - if it can be done. Alite (C3S) is the main active component of clinker, and the new process is designed to optimise the cooling and composition of the slag to create a high proportion of alite in the final steel slag. The ratio of SiO2 and CaO must be optimised to form alite, while MnO content must be between 1-5% and the MgO content must be below 5%. The cooling time of the slag should be on the scale of seconds to minutes. The beneficiation of the slag starts when it is still molten, through the reduction of iron oxides in the slag through the introduction of coal as a reducing agent, during electrical heating and bottom stirring. The reduction of the iron oxides in the slag to iron metal allows high recovery of remaining metal in the molten slag. The subsequent dry solidification of the molten slag generates the crystal structure, while also allowing energy recovery from the cooling of the molten slag. The solidification can be accomplished by thin-film open dumping, with BSSF, or with dry granulation using a rotating disc. Finally, Frank said that the grinding step increases surface area and hydraulic activity, while at the same allowing further recovery of metal from the treated slag. Frank pointed out that the economics of the process are positive. At the same time, by using the steelmaking slag as an alternative steel slag clinker (or 'slinker' as it was dubbed) rather than using a normal clinker reduces the CO2 output of the final cement by 589kg.
Janice Bolen of Canadian company Hatch next spoke about recent developments in the Ecomaister-Hatch dry slag atomisation process. Janice suggested that water granulation of slag involves complex system design, high use of water, has explosion potential and pollution potential. Dry slag granulation avoids many of these downsides, through using high pressure air to atomise the molten slag. This creates a different product from water granulation, the so-called 'slag balls,' which can be used for abrasive blasting, road pavements, concrete materials and as a sand replacement. The Ecomaister system allows heat recovery of the post-atomisation heated air. Lab scale testing has been undertaken on a wide variety of slags from around the world, and the company has also developed mobile suitcase-size and shipping container-sized test rigs. Stainless steel AOD slags are notorious dust-producers, from free lime generation and hydration and from the dicalcium silicate beta to gamma transition which causes volume expansion and crystal disintegration. By rapidly cooling the slag through the 490C phase transition temperature through slag atomisation, the crystal disintegration can be avoided. The process is used in a number of steelworks in Korea and India.
At the start of the next special session on the slag research of the FEhS institute for building materials, the director of the institute, Thomas Reiche, introduced the organisation. The FEhS provides research, consultancy and advocacy for slags and by-products, with 37 member companies from the steel, cement and slag processing industries. Over 20 research projects are currently running on building materials, based in its six laboratories.
Henning Schliephake of EAF steel-maker Georgsmarienhütte GmbH spoke about the company's NoWaste strategy. He pointed out that a change in German environmental regulations would mean that if the company's slag disposal strategy was continued, then it would be hit with a bill of over Euro2.5m each year. Business as usual is not an option, since in the future landfill will not be economic. Chrome, manganese and vanadium oxides are all present in EAF slag and can be a challenge for further use of the slag. Boron and phosphorous addition to LF slag can bring problems if any portion of the slag is returned to the steel-making process. Dry solidification can be used, with the EAF slag being reused as a slag former instead of limestone. The company pioneered the use of inclined copper plates for rapid cooling of EAF slag. Henning Schliephake pointed out that viscosity of a slag will increase as metal is recovered, meaning that to retain the same viscosity the slag will need to be heated. EAF slag will also need to be dephosphorised. However, if the EAF slag can be reduced in the direction of the composition of BFS, then it can be more readily used. He pointed out that the reduced EAF slag cannot be reused in the EAF, but can be used in other metallurgical processes, since it essentially already has the composition of a steel alloy. He concluded, "Steel workers do not only produce steel meeting the highest requirements of their customers but also byproducts with an intrinsic value of which they are often not aware."
Volkert Feldrappe of the FEhS underlined the importance of the industry and pointed out that the volume of raw materials used in cement production in Germany each year would fill up the Pyramid of Cheops, twice. Volkert pointed out that the vast majority of possible compositions of 'cement' have not been standardised. However, there is now a recognised European procedure underway to try to standardise the composition and properties of these possible compositions, which are combinations of OPC clinker, flyash, GBFS, pozzolans, silica fume and limestone. On the basis of just a ternary mix of clinker, ash and slag, mathematical models of mortar strength development can be shown to be highly accurate, when other strength-influencing factors such as particle size and reactivity are carefully controlled.
David Algermissen of the FEhS gave the final presentation on the first day, on the metallurgical conversion of EAF slag to form a beneficial material for the cement industry, as part of the Klinkeos project. In the future, German regulations will place EAF slags into three categories, with only 15% in class 1 which will not be considered a waste. Classes 2 and 3 will be considered waste and will not be allowed for use. David spoke about the reduction of EAF slag using carbon and/or FeSi additives, but initial experiments created 'falling' slags that disintegrated with the C2S beta- to gamma mineral phase transition. Addition of too much lime to the EAF avoided the problem of falling slags, but led to highly viscous slags with free lime. Careful attention of the amount of lime addition was critical to creating a slag that was useable as a clinker replacement in the cement industry. Another option was to add silica, to create a material with the composition of GBFS. Although this is indeed possible, the process has a high energy demand, requires conditioning chemicals such as lime and produces a poor quality metal, while at the same time being sensitive to the reducing/conditioning times. Further work on this promising area of research is required.
Global Slag Awards
The Global Slag Awards Dinner took place at the Classic Remise classic car centre in Düsseldorf, featuring a locally-sourced menu, German beers and classic jazz. The Global Slag Awards were presented at the dinner, with the Global Slag ‘company of the year’ award going to Harsco Metals & Minerals. Slag equipment supplier of the year was awarded to Loesche GmbH, ‘plant of the year’ went to Phoenix Services’ Burns Harbor slag handling plant near Chicago, ‘product of the year’ went to Umicore’s battery recycling slag, ‘slag user of the year’ was awarded to Cemex and the ‘technical innovation’ prize was awarded to the FEhS in recognition of its work on slag research. The Global Slag ‘personality of the year’ award - equivalent to induction into a kind-of Global Slag ‘hall of fame’ - went to well-known slag grinding expert Caroline Woywadt, of Gebr. Pfeiffer.
Second day
On the second day, Caroline Woywadt of Gebr. Pfeiffer started the session on slag grinding advances with a case study of slag grinding in the world's largest cement mill at Barroso in Brazil. Caroline pointed out that without knowledge of the grindability of the slag, the output of the vertical roller mill cannot be calculated. Extensive testing of the slag must take place to enable effective engineering and design of the mill. The Barroso plant chose an MVR 6700 C6 mill from Gebr. Pfeiffer, on the basis of its lowest capex. The grinding table is 6.7m wide, with six rollers, each with 2.7m diameter. There are six 1950kW drives in a 'MultiDrive' setup. The mill can produce up to 450t/h of 34% slag cement at 4420 Blaine. The mill has the possibility of operating with fewer than six rollers, and with fewer than six drives.
Winfried Ruhkamp of Loesche next gave a paper on the mobilisation of hydraulically active phases in steel (LD) slags through the production of ultra-fine material. Winfried pointed out that there are huge quantities of steel slags worldwide with low technological and economic value, while at the same time the demand for cement is ever-increasing. In a study, LD slags were shown to contain clinker-like mineral phases such as alite and belite, but also significant quantities of unusual phases such as srebrodolskite, Ca2Fe2O5. An XRD study of LD slags suggested that the amorphous phase was in fact a 'crypto-crystalline' belite phase. Additionally, belite is often overgrown with inactive phases such as magnetite and wustite. These otherwise non-reactive phases could be activated through ultra-fine grinding. The highest-fineness LD slag sample demonstrates strength nearly as high as CEM I. Winfried Ruhkamp pointed out that the particular grinding mode in a VRM means that a different pattern of cracking of crystals allows a higher strength development compared to grinding in ball mills. In some cases, a coarser fraction of the VRM-milled slag demonstrated a higher strength development. This was found to be because the coarser fraction was enriched in the belite mineral phase, whereas the amorphous crypto-crystalline belite phase was enriched in the finer fraction. It was found that the LD slag with the slowest cooling had the lowest content of crypto crystalline belite, and this slag had the highest strength development response to fine grinding.
Bunpei Suzue of Kawasaki Heavy Industries (KHI) of Japan introduced delegates to the CK vertical roller mill, which is already in use for cement and slag grinding in plants around the world. The second generation CK mill features a modular design of rollers and roller arms to reduce construction costs, a low-vibration concrete pedestal (contrasting with the steel pedestal of the first generation mills) and hard-facing on the tyres and table. KHI has a manufacturing facility in Wuhu, China, capable of producing 18 CK mills each year. Bunpei Suzue pointed out that two CK 450 mills have the same output as a CK 610 six roller mill, using 50% less equipment and nearly 20% lower overall cost. Finally, he gave some details of a counter-weighted movable material bed stabiliser used to de-aerate the material bed before the rollers, which led to some improvement in production rate or reduction in specific energy consumption compared to a fixed bed stabiliser.
Next Stefan Seemann of Humboldt Wedag gave a comparison of high pressure roller presses and VRMs for slag grinding. In a roller press, one roller is fixed while the other is mobile and is pressed using an hydraulic system to provide the grinding force. The roller press can be combined with static and/or dynamic separators to achieve high recovery of pig iron in slag grinding, while at the same time providing high grinding fineness. Stefan suggests that roller presses use around 3-5kWh/t less compared to a VRM to grind slag to the same fineness, or, using the same specific energy consumption can grind to a much higher fineness. Both systems have the same heat consumption. However, there is a very large difference in service life, with the stud lining of the roller press having a lifetime of 25-40,000 hours, compared to perhaps a tenth of this lifetime for wear surfaces in a VRM. Civil costs are also around 10% lower with a roller press, according to Stefan Seemann.
Adam Reid of Yara next gave a presentation on the impact of calcium nitrate (CN) on the setting behaviour and strength development of OPC and slag-based blended cements. CN has traditionally been used as a set accelerator for concrete setting in cold weather, as well as an accelerator for the precast industry to increase production. Blended cements featuring slag (and flyash) typically suffer from retarded strength development. Adam showed that addition of CN to flyash blends accelerated hydration and decreased the heat of hydration, while compressive strength was not significantly affected. In the same way, setting times were reduced with GBFS dosed with CN. The effect was greater at higher ambient temperatures (20°C) compared to lower temperatures (5°C). Beyond 4% dosage some deleterious effects were seen on compressive strength development.
Patrick Ullrich of MAPEI GmbH spoke about performance improvement of BFS blended cements. The most suitable slag for use in cement plants is that with the most hydraulic reactivity, which is controlled by its basicity ((CaO+MgO)/SiO2 - higher is better) and a high glass content. Three categories of cement additives may be employed to improve the performance of slag cements: pure grinding additives, grinding additives which also have a chemical effect on strength and performance enhancers which allow the reduction of the clinker factor. In some ball mills, the balls may become coated which decreases grinding efficiency, while agglomeration of fine particles reduces the efficiency of the classifier. Through the reduction of charges on the particles, agglomeration can be reduced with concomitant increases in grinding efficiency. Additives can also be used to improve 'dry flow,’ for example to avoid problems in transport from mill to silo and allowing faster loading from the silo to the truck. Performance enhancers can be used to increase the production of a grinding unit or to provide the same strength development at a coarser level of grinding.
Els Nagels gave the final presentation at the conference, on how to produce quality products from non-ferrous slags. Previously the approach might have been 'what is the composition of the feed materials and what strength will we thus achieve in the final product?' However, recently a different approach has been pioneered, on the basis of 'what strength do we require and hence what composition of feed materials do we need to choose to achieve this?' Els pointed out that practically every characteristic of the final slag can be calculated in advance, including its viscosity, the expected minerals in the slag after cooling and the hydraulicity and activation possibilities. Non-ferrous slag-forming processes typically have lower temperatures and iron must be thought of as the primary reactive ingredient that reacts with contaminants to form a slag. Els pointed out that if the metallurgical industry wants to sell solidified slag as a product then it needs to be treated as a product and if the construction industry wants to use slags as a raw material, then it needs to define the specifications of the slag product inputs. However, Els suggested that Portland cement-like chemistry can never be achieved from non-ferrous slags. Slag engineering is possible, with chemical slag stabilisation and with ‘cleaning’ of slags through the removal of Pb, Zn and Cu. The mineralogy can also be controlled by altering the cooling profile. Spark software can be used to forecast cooled slag mineralogy and final mechanical properties. Slag can also be used as a base ingredient (with soluble sodium silicate (‘water glass’) and sand/rock) to form an inorganic polymer which has respectable compressive and flexural strength. Els concluded that slag engineering can be accomplished if the will exists.
Farewell and prizes
At the end of the conference, a number of prizes were awarded. Ralf Perret of thyssenkrupp Industrial Services was voted to have taken the best photo submitted in the Global Slag Photo Competition 2017, while Loesche was awarded the prize for the best exhibition stand. In the best presentation awards, Winfried Ruhkamp of Loesche was third for his paper on the mobilisation of active phases via ultra-fine grinding; Stefan Seemann of Humboldt Wedag was second for his paper on a comparison between roller presses and VRMs; and Els Nagels of InsPyro was the winner of the best presentation award for her in-depth paper on slag engineering and design - the conference had obviously saved ‘the best until last.’
The conference was highly praised by delegates for its mix of networking and technical content.
Global Slag Conference field trip to Dyckerhoff's Lengerich cement plant - Wednesday 17 May 2017
Photos courtesy Peter und Lochner, Aerzener Maschinenfabrik
