Döner fırında katı esaslı redükleyici kullanılarak sünger demir üretimi

Abstract

Demir oksitli cevherlerin, katı veya gaz esaslı redükleyiciler kullanılarak, bir şaft fırını, akışkan yatak veya döner fırında redüklenmesi sonucunda üretilen metalik demir oranı yüksek, gang oksidi düşük ürüne, sünger demir veya direkt redüklenmiş demir adı verilmektedir. Günümüzde, kullandıkları redükleyici tipine göre, sünger demir üretim yöntemleri, gaz ve katı esaslı olmak üzere, iki ayrı ana grupta toplanmıştır. Mevcut yöntemlerle, yılda yaklaşık, 14 milyon ton sünger demir üretilmekte ve bazik oksijen konverterlerinde soğutucu olarak kullanılmasının yanısıra, esas olarak, elektrik ark fırınlarına şarj edilmektedir Tez çalışması bünyesinde yapılan deneysel çalışmalar da, sünger demir üretimine uygun koşulların saptanması amacıyla Cp.^/FeTopl tüketim oranı, sıcaklık ve süre olarak, çalışma parametreleri seçilmiş ve bu parametrelerin sünger demir üretimine etkileri incelenmişti*'. Redüksiyon deneyleri, bölüm 4 2.1 de anlatılan laboratuvar tipi döner fırında gerçekleştirilmiştir. Fırın dan belirli zaman aralıkları ile numuneler alınmış ve bunlar kimyasal analize tabi tutulmuştur. Kimyasal analizlerden, numunelerin metalik ve toplam demir içerikleri bulunmuştur. Metalik ve toplam demir miktarlarından hareketle, metalizasyonlar hesaplanmıştır. çalışma parametrelerinin metalizasyona etkileri, gerek değişik deney şartları için, metalizasyon değişim eğrilerinin çizilmesinden ve gerekse, değişik numunelerin mikroyapı fotoğraflarının çekilerek incelenmesinden yola çıkılarak saptanmıştır. Her iki durumda elde edilen sonuçlar, tezin son bölümlerinde verilmiştir. Deneysel çalışmalardan elde edilen sonuçlar değerlen dirildiğinde, sünger demir üretimi için, optimum çalışma parametrelerinin verilmesi mümkündür. Tüketim oranı 0.40 ve sıcaklık 1000°G seçildiğinde, 90. cı dakikada % 97 metalizasyona ulaşılmaktadır. Bununla birlikte, redüklenmiş numunelerin metalizasyonlarının ortalaması alındığında metalizasyon % 93 olmaktadır. Bu değer, endüstriyel Uygulamalar için verilen değerlerle uyum sağlamaktadır. - v - SPONGE IRON PRODUCTION IN THE ROTARY TUBE FURNACE BY USING SOI-ID REDUCTANT SUMMARY Sponge iron is in use more than 100 years. The first sponge iron production plant was established in Britain in 1873 but, shut down after 4 years operation. The main developments on the process were carried out after 1970*8. Up to date» lots of sponge iron production processes were developed but, only fewer processes succeeded in continuing to the production of sponge iron. Sponge iron or direct reduced iron is produced by reducing the iron ores or pellets in a reactor, a shaft furnace or a rotary furnace in the solid state. Its metallic iron content is high and gang oxide is low. This product is mainly used in BOFs or EAF§; together with or instead of steel scrap* Two main types of reductants are used in sponge iron product ion i 1. Gas reductant » Natural gas. 2. Solid reductant l in general non-coking coal. Depending on the type of reductant, two kinds of sponge iron processes exist * - Gas Based Processes - solid Based Processes As can be seen, gas baöed processes use natural gas in production of sponge iron. But, the natural gas is changed into the reducing gases (GO and H,) in the gas reformers. Reformed gas is heated up and sen to the reactor in order to reduce iron oxides. Applications of the gas based processes are, Midrex Hy]>I and HyL-III processes.

Sponge iron is in use more than 100 years. The first sponge iron production plant was established in Britain in 1873 but, shut down after 4 years operation. The main developments on the process were carried out after 1970*8. Up to date» lots of sponge iron production processes were developed but, only fewer processes succeeded in continuing to the production of sponge iron. Sponge iron or direct reduced iron is produced by reducing the iron ores or pellets in a reactor, a shaft furnace or a rotary furnace in the solid state. Its metallic iron content is high and gang oxide is low. This product is mainly used in BOFs or EAF§; together with or instead of steel scrap* Two main types of reductants are used in sponge iron product ion i 1. Gas reductant » Natural gas. 2. Solid reductant l in general non-coking coal. Depending on the type of reductant, two kinds of sponge iron processes exist * - Gas Based Processes - solid Based Processes As can be seen, gas baöed processes use natural gas in production of sponge iron. But, the natural gas is changed into the reducing gases (GO and H,) in the gas reformers. Reformed gas is heated up and sen to the reactor in order to reduce iron oxides. Applications of the gas based processes are, Midrex Hy]>I and HyL-III processes. The solid based processes use non-coking coals to vi - reduce iron oxides. A rotary furnace is used as the reactor. The charge is given to the furnace from the upper end and is heated up to the reduction temperature by blowing air and injecting pulverized coal. The main example of these processes is S process. World sponge iron production is not so much in respect of sponge iron capacity.., Compared to 780 million tons of steel production, sponge iron is only produced at about 14,2 million tons (1988). It shows that the sponge iron production doesn't have an important role in steel production, yet. But, it* s been estimated that the sponge iron production will increase its market share during the next decade. It still remains in a stable production trend by increasing production slowly. Demand for sponge iron production will increase depending on the highly increasing scrap prices next years. The countries in which scrap is imported from the outside, will look for new alternatives for supplying feed materials for their ministeel plants. And, as a well known alternative, sponge iron production might be desired to close the deficit. In the present work, optimum conditions for producing sponge iron with solid reductant were investigated. In the experimental studies different operation parameters were selected being Cpix/Feıj>çpi.# consumption ratio, temperature and time, respectively.» The materials used for sponge iron production ore hematite type of pellets from Divriği concentration and pellety zing plants and, lignit coal from Tunçbilek region. The chemical compos it ions of the pellets and coal are shown in tables below, respectively. Table-1 The average chemical composition of the pellets (Weight per cent) - Fe Feo SİO2 AI2O3 CaÖ MgQ P ş 67,3 0,4 1,5 0,48 0,23 1,17 0,01 0,01 Na20 Table-*- 2 The chemical composition of coal (weight per cent). The pellets were screened to the 10-12 mm, in order to get uniformity in size. Physical properties pf the pellets are as follows ı - The porosity ı 25 % - Mechanical strength t 250 kg. per pellet. Coal was used in original shape without making any pre treatments. But, it was crushed with the laboratory type öf crushers and screened to -O.0.*?.-2.* 8 mm. particle sizes for using in the experiments* A laboratory scale rotary tube furnace was used to carry out the reduction experiments. The tube was made from high temperature resisting steel material and has a special design to permit the materials be reduced through a hot temperature zone inside. The experiments were made according to the experi mental procedure, given in Table-3. Tablets The Experimental Procedure The amount of coal CFix./^TQpl.Gha*gef Gî Required C used per kg. of Consumption * according to the pellets (in grams) Ratio reduction reaction 1008 0.48 1,5 ı 1,0 840 0.40 1,25 1 1,0 672 0,32 1,0 i 1,0 The reduction temperatures wefe selected, being 910, 950, 1000 and 1050°C, respectively. The effects of the temperature are given with the conclusions. In order to orberve the effects of reduction time on the metallization öf sponge iron, the samples were VI 11 - taken periodically from the furnace during the experi mental studies. The samples -were chemically analysed and their contents of metallic and total iron were determined, Accordingly, the metallization degrees were calculated by using the following relation. Metallic Iroii Metallization (in %) m - - « __-^- x 100 Total iron The effects of operation parameters were either determined by drawing the variations of the metallization of the samples depending on the parameters or shown by talcing mierostruetural photographs of the samples, reduced in different condition The results of the experimental studies are given as follows i !'?- The experimental studies were made by using different consumption ratios of 0.32, 0.40 and 0.48 and different temperatures. 33 % metallization degree was obtained under the conditions of 910°C and consumption ratio of 0*32. It means that this consumption ratio is not enaugh to reduce iron compl ate ly of this temperature. Beside, in the experiments made at lOOO^C reduction temperature and the consumption ratios of 0.40 and 0,48, high metallization degrees were obtained. At the same temperature and consumption ratio of 0,40, approx. 93 % metallization was determined in the 90 th minute of the experiment. However, when the variation of the metallization was observed depending on time, it's seen that the average value of metallization was about 93 %, This result is in well relation with the values of metallization, given for the industry, 2- The second parameter investigated in the reduction experiments was the temperature. From the experiments made at different temperatures, it was found that the highest metallization degrees were obtained at 1000 and 1050 C temperatures, When the metallization degrees were compared between two temperatures, it was found that there was no difference in metallizations and that 1050°C was not necessary to use in reduction experiments. Hence, the increase in temperature, increases the expence of the process, it is not preferred to use such high temperatures. As a result, it was concluded that 1000°C was the best reduction temperature for the technological applications, 3- The last parameter focused on in the experimental - IX - studies was the reduction time. It's possible to observe the progress in metallization from the figures given in sections before this article. Together with Cpix. /F®ropl, consumption ratio and temperature, when both parameters increased, it was pointed out that the reduction time decreased. For example ı in the experiments used the ratios of 0.40 and 0.48 and, reduction temperature of 1000°C, it was obtained that the reduction was finished at 90 th minute of the experiments in each case. 4- Thinking of three operation parameters together, it's possible to give the best results for sponge iron production. When the consumption ratio and the tempera ture was chosen 0.40 and 1000°C, respectively, the reduction finishes at 90 th minute with a higher metalli zation degree: At this point, approx. 97 % was obtained. In terms of technology, these values of operation are well enough.