A new type of Processing and Resource Application Technology for Baosteel Steel Slag

Transcription

1 A new type of Processing and Resource Application Technology for Baosteel Steel Slag Jin Qiang [1], Xu Jinyin [2], Gao Weibo [3] (Baosteel scientific association for steel slag researching, Baoshan Road Yueluo and No.77, Road Fasi, Slag Reasearch Center, Shanghai, , China) abstract: This article summarizes a new processing technology for steel slag in Baosteel and the slag application as second resource. The slag processing level and characters of diversification are analyzed in brief, emphasizing the necessity and original creativity of upstream management and processing revolution. The gradual achievements on the omni-directional use and the expansion of resource application technology and the application domain, based on the different characters of slag, are elaborated. Development direction of the processing & resource application technology is proposed, too. key words: Baosteel, new processing technology of steel slag, technology for application as second resource 1 Introduction Resource application is a long term strategy policy for national economy and social development.it's metallurgical industry s responsibility to enlarge recycling profit with the clean producing principle and to realize sustainable development. Emphasis on the re-application of slag raises a new scientific development view for metallurgical steel slag recycling technology. During past 20 years developing practice in Baosteel, steel slag is changed from waste into treasure, making 100% recycling rate available in the future. Recycling technology is the way for the steel slag used in a wide range. The characters of Baosteel slag show the specialty of steel slag technology, effective usage is rooted from advanced processing technology, and Baosteel s recycling technology is enriched and developed through multiple processing methods. 2 Development of the new processing technology in Bao-steel 2.1 The introduced and advanced I.S.C tray way I.S.C tray way of Baosteel is a patent technique imported from Japanese Deafen steel plant when Baosteel was first put into production, which belongs to slag hot splashing system. By this technology, the fluid AB slag with 1500 is put into a flat plate, cooled by spraying water to 700, and cracks generates naturally. Then the slag on the flat plate is poured into slag car after it is cooled by water to 200 and again poured into a pool for the third cooling step. Finally the slag is fished out of the pool at below 100. This line has three water-cooling steps but the temperature around is still as high as 100, so a remote controller must be equipped. Therefore, the operator has good and safe working condition without dust but just some white vapour. This technique is high mechanization and automatization with little pollution. 2.2 Originally creative and revolutionary BSS method with short process BSS method is called box tumbling method, which is a new slag processing technology imported from Russian Ural Steel Academe lab during Baosteel phase II steel making period. Many new technologies as stuff-in device, steel balls cooling device, tray seat adjusting device and big tooth-circle are integrated together with this slag processing line, which is the only technology put into industrialized production and also the slag processing technology with Baosteel own self-intellectual property. In the process of implementation, when the liquid slag is poured into the tumbling box along the slid slot, the tumbling box sprays water into itself with high revolving speed. Because of the special inner structure, although the water and slag go into the box at the same time, the vapor with high pressure formed by quantity of heat can be emptied from the bottom of the box, so the water cannot be airtighted by the slag to avoid explosion. When the hot slag goes into the box, slag can be broken into pieces with 90% of slag particles smaller than 10mm by steel balls because of the weak combinative strength among the slag molecules. In this way, BSS method can save many assistant devices such as particle steel works, slag car and pools so that a lot of investment can be saved. Therefore, BSS method has realized the revolutionary of slag treatment technology, which represents the direction of slag treatment technology. Baosteel has implemented the strategy of the the technology transfer and industrial manufacture. 2.3 Expending the domain of Sealed Container Method Sealed container steel slag processing technology is introduced from Shanghai steel making No. 5 factory in The principle of this processing technology is the application of the remaining heat in the slag. After adding cool water, the water turns into steam in the sealed container, thus decomposes the f. CaO in the steel slag. The higher temperature of the slag in the container, the more steam will be given, and the longer the slag and steam co-exist, the 1

2 stronger ability of the steam immerging into slag is gained, and therefore,at certain pressure, the decomposition effect for the f.cao in the steel slag is maximized. Baosteel possesses two sealed container lines in No.1 and No.2 steel-making plants. No.1 plant mainly processes D slag from I.S.C works and the casting-remained slag, which is called slag sealed container line. Through the industrialization production, pulverization rate was enhanced for the steel slag greatly, which plays the huge role for guaranteeing the application and production for the returning burned slag. No.2 plant processes all kinds of slag to supplement the sealed container so that slag treatment devices are in full use, enhancing the environmental protection in iron slag production. Table 1 comparison between I.S.C and BSS in technical &economic index serial number items of comparison between I.S.C and BSS I.S.C BSS 1 investment high about one third of I.S.C. 2 many serial simple equipment equipment 3 plant possession area comparably long one third of I.S.C 4 running, fix fee high comparably low 5 operation period comparably long short flow 6 environmental control for emission low high 7 invariability(f.cao in finished product) low high 8 hardness low high 9 separation efficiency for the iron from the slag low high 2.4 Slag container-separate bar new technology in metallurgical (New original creative environmental protection technology in dregs steel and iron recycling use) The casting-remained slag is formed in the steel ladle with more alumina. When the casting-remained slag is poured into the steel ladle, big slag blocks are formed at the bottom of the ladle, which can be reused after exploding, cutting and breaking. Through putting all-slag concrete clapboard in the container, the remainder steel will not form big slag blocks but be in proper size before returning into the furnace. Since the new technology was put into practice two year ago, the size and weight of the slag steel all reach the request of reusing in the furnace so this technology not only avoids the formation of slag blocks, saves resource and reduces the cost of treatment, but also completely eliminates the dangerous conditions, reduces the pollution and makes contribution to promoting environmental protection technology in dregs steel and iron recycling production and realizing the casting-remained technology revolution. It is estimated that more than 100,000 m2 of the land can be saved. 2.5 Developing wet treatment technology (Promoting the level of iron slag processing environmental protection) The iron slag is formed before the furnace iron slag goes into the converter, caused by the development of clean steel production technology, and manifests the entire dregs processing technological development, and becomes the major object of future slag treatment. Wet treatment technology is developed at Baosteel after a lot of practices. Before the slag jar bends to the drop hammer works, large quantity of water is poured into the slag ladle to make slag and iron in the slag ladle be cooled simultaneously to , then slag ladle can be poured. This technology not only gets rid of floater but avoids the potential explosion problem, which is a big development of slag treatment technology. During the development in past 20 years, Baosteel has made great achievements in introduction, digestion, and absorption of technology, such as the advancement of slag treatment technology and the development of resource application technology. 3 Baosteel Resource Technology Baosteel various treatment technologies create different properties of slags. Through 10 years of hard work, Baosteel not only changes the scene of slag disaster at the first stage of production, but implements recycling, processing and management by sorts which achieves improvement of slag resource application. 3.1 The main kinds of Baosteel slag and its properties Table 2 basic characters and productive volume of Bao-steel steel slag serial basic properties kinds of slag number activity stability hardness a.yield(10,000tons) 1 Iron slag good bad good 10 2 D slag good bad normal 40 3 water-cooling slag good good normal 35 4 converter slag bad best best 5 5 casting-remained slag normal bad normal 10 2

3 Table 3 lithofacies comparison between I.S.C and BSS name CaFeO 4 CaO.FeO C 2 S C 3 S alit 2(FeO)SiO 2 flat plate slag converter slag Slag used as metallurgy raw materials returning to manufacturing Slag smaller than 5mm charged into the sinter in place of flux can not only recycle many components such as refined mine powder, TFeO, CaO, MgO, MnO and other rare elements but can be the intensifier to improve the quality and productivity of the sintering ore. Slag replacing limestone as the flux in BF can take advantage of useful elements in slag, saving the consumption of flux, improving the fluidity of BF slag, increasing iron production. In converter, per ton of liquid steel consumes 25 kg returning slag, together with dolomite, which makes slag form earlier, reduces the erosion of slag on furnace liner, prolongs furnace life span, reduces consumption of refractories, furthermore, collecting and distilling rare elements in slag. Partial slag s recycling in- house is placed important place and used widely. However, different ore mix technology has different requirements on usage of resinterring. Overuse can result in the richening of the harmful elements such as S and P. The application of resinterring in Baosteel began from 1996, which was decided after accurate calculation and many experiments. At present, the content of slag in the sintering is 1.2%, with average particle of 1.3, and the application amounts to 150,000 tons. 3.3 Slag baking cooked materials in cement raw mixture The content of CaO, SiO 2 and Fe 2 O 3 is very rich in slag with total portion of 75%, which are used as iron emendation in the raw materials of cement. The slag is comparatively cheap and therefore used widely in the cement industry in China, which is mixed by less than 10%. The cement technology is baking cooked mixture by using limestone, and 440 kg CO 2 is produced when decomposing 1ton of limestone requiring 500 thermo of heat while 1ton of cooked mixture of cement requires 230kg coals. After 10% slag is added into the raw mixture of cement, much limestone and coal are saved every year. However, it still needs baking, which cannot eliminate the negative influence on environment. Although it has good market now, the economical and social benefits are not obvious. 3.4 Slag powder The research on slag powder application is a hot issue home and abroad during recent years. The main resultant of slag in the converter are olivine, rhodonite and C 3 S C 2 S. C 3 S and C 2 S are active in water, and f.cao can also strengthen cement to some extent. When the slag is grinded to the 4500cm 2 /kg, it can replace 20% of cement equivalently in commercial concrete mixture. When it is added with furnace slag powder and coal powder, the effect can be doubled. The concrete made by D slag powder has advantages of good wearability, low heat generation which is the development direction of high performance concrete. The mechanism of excitation of slag after being pulverized comes from ultra fine grinding which brings material and crystal structure as well as the surface properties into restructuring and forms inner energy and surface energy, improving activity of the concrete in hydration period. serial number thickness Table 4 testing result for activity of complex steel slag powder (tested by construction academy of science in Shanghai) early setting time final setting time water cement ratio fluidity content of requiring water FSO strength activity shrinking 3d 7d 28d 3d 7d 28dwater ratio :05 3: / / / GF :35 3: / / / GF :00 4: / / / GF :20 3: / / / GF :15 4: / / / GF :25 3: / / / GF :25 4: / / /

4 Table 5 Bao-steel non-shamotter concrete cement testing results Remarks: the upper complex steel slag powder has 2% of riddle remainder and eligible stability. the influence of slag powder fineness and content on the concrete mechnics properties 60 28ds compressive strengt m2/kg 500m2/kg 600m2/kg 0 0 content of slag powder Table 6 the effect on concrete mechanism by fineness& productiion of steel slag powder items of tests slag road cement standards results of tests density per basic surface area 380m 2 /kg 466 elementary setting time 1h 5h and 20min final setting time 10h 7h stability eligible eligible bending strength(3d) 2.5MPa 4.5 bending strength(28d) 5.5MPa 9.4 stressing strength(3d) 11.0MPa 18.6 stressing strength(28d) 32.5MPa 45.2 Although the mechanism of Slag after being powdered as mixture of concrete is is in the scope of gluteus materials, the application technology of resources is different. The powder technology not only eliminates the homogenized quality due to the different grinding performances among the mixture of cement raw materials, but also lowers CO 2 emission and is changed into new building materials which will generates high additive benefits. Therefore, the slag powdering technology is a collective embodiment of slag resource application technology transferring into productivity, which presents the overall development of the slag resource application technology. Although this technology is in the phase of development, it has great potential after being improved continuously.. Meanwhile, with the advancement of the industrialization of converter treatment, the potential properties of high rigidity and good stability make slag a good new martial. 3.5 The exploration of the ecological concrete The application of the optimized container proves that the complete metallurgical slag products can be widely spread and applicated in the metallurgy industry. The improvement of the optimized container technology provides an effective platform and carrier for resource application technology, directly promoting the development of slag powder, slag glutinous materials and slag products and other technologies. With the interaction between slag powder and furnace ore powder, by adding gypsum as intensifier, high performance concrete which totally meets applicable requirements can be made. Based on this fundamental material, according to different usages, road concrete, seashore concrete can be produced. The slag-made road concrete has merits of bending-resistance, tensile resistance, wearability, penetrating-resistance, which can improve the adhesion of halobios if used in marine engineering concrete. These applications fully dig out the natural properties of high 4

5 alkalinity of slag, which have positive meaning in marine ecological treatment. 3.6 The constructing use study of new building materials According to the beneficial physical and chemical properties of partial slag, Baosteel has many engineering examples such as wearable ground and so on. The marble with 70% of slag content has super wearability, hardness, heat-resistance, and lower content of radioactive elements, compared to orther artificial marble. GRC products with slag not only meet the standards of the same kind of quartz with high added value, but expand new approaches of slag in environmental engineering field. appendix picture 4: polymer grinding-resistant level ground by slag appendix picture 5: GRC man-made stones by slag In all, with sustainable development of Baosteel in new century, Baosteel resource application technology must be innovative and developed further on the basis of the continuous creation of slag treatment technology and continuously composes chapters of harmony between resources and the environment. Table 7 character comparison between man-made and steel slag marble names of test items and units references of tests slag marble results of tests natural marble(determinant standards ) man-made marble bulk density g/cm 3 GB/T water absorption ratio % GB/T dryness shrinkage strength, MPa GB/T dryness bending strength, MPa GB/T References 1. The treatment and resource application technology for residue in metallurgy industry, by Sunshubin and Zhuguilin, In metallurgy Industry publishing house, 2003; 2. Industrial slag manufacturing and building materials technology,by Yanzhenjia, Heyanjun and etc., the chemical industry publishing house, 2002; 3. High Performance Concrete, by Wuzhongwei, China railway publishing house, 1999; 4. The cement industry grinding technique technology, by Wangzhongchun, China building industry publishing house,2000; 5. The development and use of converter slag in sintering and building industries, by Sunjunbo; 6. The treatment and comprehensive application of slag, by Wuxizhe; Introduction of the first author: Jin Qiang, born in April, 1965,now acts as the director of the research and development department of SBMCC, owns the senior management title, has been engaged in the study for resource and environment for many years and has obtained fruitful progress. Address of unit: Baosteel scientific association for steel slag researching, Baoshan Road Yueluo and No.77, Road Fasi, Slag Reasearch Center. Postcode: Tel.(Fax): M.P: baoyedd@online.sh.cn 5