Entegre demir çelik tesislerinden ortaya çıkan katı atıkların değerlensirilmesi
Başlık çevirisi mevcut değil.
- Tez No: 75292
- Danışmanlar: PROF. DR. SÜHEYLA AYDIN
- Tez Türü: Yüksek Lisans
- Konular: Metalurji Mühendisliği, Metallurgical Engineering
- Anahtar Kelimeler: Belirtilmemiş.
- Yıl: 1998
- Dil: Türkçe
- Üniversite: İstanbul Teknik Üniversitesi
- Enstitü: Fen Bilimleri Enstitüsü
- Ana Bilim Dalı: Metalurji Mühendisliği Ana Bilim Dalı
- Bilim Dalı: Belirtilmemiş.
- Sayfa Sayısı: 119
Özet
Metalürji sektörünün büyük bir kolunu oluşturan entegre demir çelik tesislerinde çelik üretiminin gerçekleştirildiği yöntemlerin çeşitli aşamalarında ortaya çıkan atıklar, ortadan kaldırma sorunlarına ve özellikle de çevre kirlenmesine yol açmaktadır. Son yıllarda entegre demir çelik tesislerinden ortaya çıkan bu tip atıkların hem çevreye zarar vermeden bertaraf edilmesi hem de içerdiği demir oksitlerin kazanılması amacıyla yapılan çalışmalar yoğunluk kazanmıştır. Bu çalışmada ülkemizdeki entegre demir çelik tesislerinden biri olan Ereğli Demir Çelik Çelik Tesisleri'nde (Erdemir) ortaya çıkan demir oksit içerikli atıklardan yüksek fırın (YF) ve bazik oksijen fırını (BOF) tozu ve çamurunun, kaba ve yağlı hadde tufalinin soğuk bağlı pelet ve sünger demir üretimiyle değerlendirilmesi amaçlanmıştır. Soğuk bağlı pelet üretimi deneylerinde klinker ve klinkerle birlikte YF cürufu bağlayıcıları kullanılarak doğal, hızlandırılmış ve doğal + hızlandırılmış yaşlandırma şartlarında soğuk bağlı aglomerasyon için uygun bağlayıcı ve yaşlandırma ortamı belirlenmeye çalışılmıştır. Belirlenen soğuk bağlı aglomerasyon şartları kullanılarak empüritelerin sınır değerlerde tutulduğu atık karışımdan peletler üretilmiş ve üretilen peletlerin indirgenebilme kabiliyeti incelenmiştir. Deneysel çalışmalar sonucunda YF için kritik olan empüritelerin sınır değerlerde tutularak hazırlanan atık karışımın, hem mukavemet hem de indirgenebilirlik açısından uygun olan % 4 klinker + % 6 YF cürufu bağlayıcı karışımı kullanılarak aglomerasyonuyla üretilen soğuk bağlı peletlerin YF'da şarj malzemesi olarak değerlendirilebileceği saptanmıştır. Atıkların tesislerden ortaya çıkış miktarına göre hazırlanan karışımdan sünger demir üretimi deneylerinde kok ve grafit tozu indirgeyicilerinin ve miktarlarının, zamanın ve sıcaklığın indirgenme oranına etkisi incelenmiştir. Deneysel çalışmalar sonucunda yüksek indirgenme oranlarına ( > % 85 ) sahip sünger demir üretiminin, % 15 kok tozu kullanılarak 1100°C'de 105 dakika, % 20 kok tozu kullanılarak 1050°C'de 105 dakika ve 1100°C'de 90 dakika indirgenmenin sonucunda gerçekleştirilebileceği saptanmıştır. Kok tozunun indirgeyici olarak kullanıldığı sünger demir üretiminin temel prensibi olan indirgenmenin, kinetik incelemesi sonucunda indirgenmenin Ginstling- Brounsthein modeline uyduğu yani indirgenmenin yayınma kontrollü olduğu saptanmıştır. Sünger demir üretiminde % 15 ve % 20 kok tozunun kullanıldığı indirgenme deneylerinde aktivasyon enerjisi ~ 51000 joule/mol olarak hesaplanmıştır.
Özet (Çeviri)
Industrial ecology means the study of materials and energy flows within an industrial eco system, with the ultimate objective of finding ways to better minimic nature so that waste streams are eliminated. In the iron and steel works that forms the biggest part of the metallurgy sector, wastes which are generated during the different stages of steel production from ore or scrap cause disposal problems and especially environmental pollution. For the iron and steel industry, recycling is preventing and minimising of generated wastes, reusing of wastes by processing inside or outside of the plants and reusing of heat that generates from production stages and waste processing. Industrialised country group's studies about the protection of environment are markedly increasing. As a result of governmental policy in U.S, water and air pollution have been prevented which is resulted in significant reduction of particulate emission ( mg/m3). In U.S, 15 % of the new capital investments consist of developing and establishing environmental control systems. The same conditions are also valid for Western Europe and Japan. Especially in Japan iron and steel works, which have been established during last two decades, took action to prevent environmental pollution. Table 1 shows the unresolved environmental problems in the iron and steel industry. Table 1. Unresolved environmental problems in the iron and steel industry * NOx and SOx emissions by sinter plants * Emissions by coke plants * Treatment of blast furnace (BF) sludges * Treatment of basic oxygen furnace (BOF) sludges * Treatment of rolling mill wastes * Treatment of electric arc furnace (EAF) dust * Treatment of pickle liquor wastes * Ironmaking and steelmaking slags * Waste oils and greases According to Table 1 integrated iron and steel works causes basic environmental problems. Although coke and sinter plants can be brought into compliance with the current regulations because of budgets for environmental preventions and storing of generated wastes according to the environmental regulations cause increasing of production cost. In the mini-mills that produce steel from scrap by the electric arc furnaces (EAF) dioxin formation at high frequencies isimportant unresolved problem. Indeed production of steel with EAF in mini-mills causes less environmental problems compared to the integrated iron and steel works. Other countries apart from the industrialised ones; that cover the half of the world steel production are also currently working on the environmental problems. In Korea, Taiwan and Mexico, new plants and plants are being constructed suppose to have their environmental preventions in the construction stages. Although in China environmental pollution control are not being in sufficient level, in some new plants environmental issues are having importance compared to past. After collapsing of Soviet Union, the steel production of Eastern Europe and Russia has been drastically reduced. Using old production technologies and insufficient local environmental regulations are resulted in serious health problems on steelworkers and pollution problems in nature. So as to prevent this situation in Russia and Eastern Europe international iron and steel comities make studies to prevent environmental pollution by technical aids. But because of the political, economical and technological factors this process could not be accelerated. Until last decade slags, dusts and sludges which are generated from iron and steel production were used to called as“waste”, but presently this concept has been changed as“by-product”due to intensive reusing of these wastes. In a typical integrated iron and steel works 420 kg of by-product is generated per ton of hot metal produced. Today so as to dispose and reuse of wastes, 20 $ per ton of steel produced in the integrated iron and steel works and 5-10 $ per ton of steel produce in the mini- mills spend. Table 2 shows a statically investigation that was carried out by International Iron and Steel Institute (TISI) about the important wastes that are generated in the iron and steel works and mini-mills. Table 2. Recycling or reuse of various steel plant wastes * Per ton of crude iron and steelAs can be seen from Table 2 solid wastes are generated in different production stages from ore preparation to rolling. The big part of the generated solid wastes consists of slag, dust, sludge and mill scale. Figure 1 shows the solid wastes that are generated during the different stages of production in a typical integrated iron and steel works. Iron Ore Hot Metal Rolling - Ö- Coarse Mill Scale Oily Mill Scale Ingot Casting Continuos Casting tt Coarse Mill Scale Oxygen Converter ç Dust Sludge Slag Desulphurization tt Slag Figure 1. Solid wastes that are generated in the iron and steel works In the integrated iron and steel works, material flow begins with the ore preparation. After the delivery of raw materials, dust is generated during breaking and screening. Moistening reduces this dust and all of the dust is reused in the sinter blend. After ore preparation in the sinter plant, dust and wastes that are generated in the plants are beneficiated. In recent years using of dust and sludge type wastes are restricted due to the reduction of the particulate emission limit value to 50 mg/m3 by regulations. On the other hand oily mill scale can not be used due to formation of fires on the filter apparatus. By using dust catcher and cyclone in BF and by using washing towers dust and sludge are generated. In 1950's 150 kg of dust and 40 kg of sludge per ton of steel produced are generated but by improving raw material preparation, charge and operation technologies, today 10 kg of dust and 15 kg of sludge are generated. In BF, slag associated with hot metal consists of 15-35 % of solid wastes is generated. In 1950's 700 kg of slag per ton of steel produced is generated but by using high-grade raw materials and improving raw material preparation, today 250 kg of slag is generated. Hot metal produced in BF is delivered to desulphurization plant so as to refine from sulphur by using soda ash, calcium carbide, lime and magnesium and slag with high sulphur content is generated. Dry and wet dedusting of oxygen converter gas in the process of steelmaking dust and sludge are generated. Since both dedusting processes are used together, either dust or sludge is generated.. In BOF, slag associated with hot metal consists of 22.1 % of solid wastes is generated. In 1950's 175 kg of slag per ton of crude steel produced are generated but by changing of charge composition and releasing of Bessemer and Open-Hearth processes, today 135 kg of slag is generated.Coarse mill scale and oil containing fine mill scale are generated as waste in the ingot casting, continuos casting and rolling. Coarse mill scale is directly used in the sinter blend, but oil containing fine mill scale is not used directly in the sinter blend due to the problem that cause in the electrostatic dust catcher filters in the sintering. For this reason by improving new roll bearings and lubrication systems oil content is reduced 50 %. In Türkiye, there are three integrated iron and steel plants called as Erdemir, İsdemir and Kardemir. Dust, sludge and mill scale type ferriferous solid wastes are generated during the different stages of their steel production. Some part of these wastes is reused in sinter plants and remainder is disposed of inside the steel works area. Although environmental regulations is come to force in 1983, the particulate emission value is more than 50 mg/m3 in sinter plants and disposal of heavy metal containing wastes (BF and BOF dusts and sludges) contaminate water and soil resources. The aim of this research is beneficiating solid wastes generated at Erdemir Integrated Iron and Steel Works by method of cold bonded pellet and sponge iron (Direct Reduced Iron = DRI) production. In the first step of the experimental study, waste mixture (% 65 Coarse mill scale + % 15 BF sludge + % 10 BF dust + % 10 BOF sludge) containing limit impurities for BF was prepared and agglomerated by using clinker and BF slag as binders. The effects of binder ratios and ageing conditions were examined on the strength of pellets. Chemical composition of the mixture is shown in Table 3. Table 3. Waste mixture containing limit impurities for BF, wt-% Experimental studies indicate that best cold bonding agglomeration conditions could be obtained as pellets containing 4 % clinker and 6 % BF slag, 8 day atmospheric plus 1 hour accelerated ageing at 100°C and pellets containing 6 % clinker and 4 % BF, 10 days atmospheric and 1 hour accelerated ageing at 100°C. Gakushin standard reductibility test was carried out in order to determine the effect of binder on the reductibility in BF. Reductibility tests have shown that 4 % clinker and 6 % BF slag containing pellets could be more reductible than 6 % clinker and 4 % BF slag containing pellets. According to the cold bonding agglomeration and reducitbility experiments, 6 % clinker and 4 % BF slag containing pellets were determined as the optimum binder with 10 days atmospheric and 1 hour accelerated ageing at 100°C.Beneficiating ferriferous solid wastes by the production of cold bonding agglomeration is an economically feasible process since there is no need to fire pellets and charging of pellets to BF would reduce the consumption of flux due to their high CaO content. In the second step of the experimental study another mixture was prepared representing to the generation of wastes. Waste mixture was agglomerated under optimum cold bonding conditions with coke and graphite reduction addition and without any reduction addition. Cold bonded pellets were reduced in a rotary kiln so as to produce sponge iron. The effects of reducing agents, C sx I Fe total ratio, reduction temperature and time were evaluated on the degree of reduction (R). Chemical analysis of waste mixture and reducing agents are shown in Table 4 and 5. Table 4. Chemical analysis of mixture representing to the generation of wastes, wt-% Table 5. Chemical analysis of reducing agents, wt-% The reduction experiments were carried out by using different C hx / Fe total ratios as 0.17, 0.31, 0.38 and 0.45 and at 900, 950, 1000, 1050 and 1100°C. Table 6 shows the maximum degree of reductions (%R) obtained by using different reduction agents at the reduction experiments. Table 6. Maximum degree of reductions (%R) by using different reduction agents According to results of reduction experiments, cold bonded prereduced pellets without any reducing agent had low degree of reduction due to the low C fiX / Fe total ratio. The degree of reduction by using coke was higher than graphite. So it can be stated that coke is the most effective reducing agent in the production of sponge iron.High degree of reduction ratios ( > % 85) were obtained by using 0.38 C fiX / Fe total ratio (15 % coke), 105 minutes of reduction at 1100 C and 0.45 C fiX / Fe total ratio (20 % coke) 105 minutes of reduction at 1050°C and 90 minutes of reduction at 1100°C. Sponge iron having high degree of reduction can be a suitable charge material for BOF and EAF. Kinetic study was carried out using coke reduction agent at the production of sponge iron. To obtain an initial idea of the kinetic law, reduced time pilots were used. In the reduced time pilots four commonly suggested models (chemically controlled, first order reaction, Jander and Ginstling-Brounsthein) for iron oxide reduction were used. Ginstling-Brounsthein model (Equation 1) seems to be the most appropriate to fit the data obtained from this study. This model shows that reduction process was controlled by the diffusion of the reaction gas. k. t = constant [ 1 - 2/3. R - (1 - R)2 ' 3] ( 1 ) Kinetic data was analysed to find the activation energy. By using 15 and 20 % coke the activation energy for reduction was ~ 51000 joule/mole.
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