Sıvı ham demirdeki silisyum miktarının torpido içerisinde azaltılmasına yönelik çalışmalar
The study about decrease of hot metal silicon content in torpedo car
Yazar: KEREM DOĞAN
Danışman: DOÇ. DR. CEVAT BORA DERİN
İstanbul Teknik Üniversitesi / Fen Bilimleri Enstitüsü / Metalurji ve Malzeme Mühendisliği Ana Bilim Dalı / Üretim Metalurjisi ve Teknolojileri Mühendisliği Bilim Dalı
Derece: Yüksek Lisans, 2018
Konu: Metalurji Mühendisliği = Metallurgical Engineering
Dizin: Bazik oksijen fırını = Basic oxygen furnace ; Demir çelik endüstrisi = Iron steel industry ; Demir çelik sektörü = Iron steel sector ; Erimiş metal = Molten metal ; Metal-silisyum = Metal-silicon ; Sıvı metaller = Liquid metals ; Yüksek fırın = Blast furnace ; Üretim metalurjisi = Production metallurgy

Özet:
Entegre çelik tesislerinde yüksek fırında üretilen sıvı ham demir çelikhanenin talep ettiği kimyasal analize ve sıcaklığa sahip olmalıdır. Sıvı ham demir kimyasal analizinde bulunan silisyum bu kritik elementlerden biridir. Sıvı ham demirde yer alan silisyumun büyük bölümü çelik üretiminde kullanılan konvertörlerde üflenen saf oksijenle yanarak silisyum dioksite dönüşmektedir. Bu yanma sırasında açığa çıkan yüksek enerji, sıvı ham demirle birlikte çeliğe ilave edilen hurdanın eritilmesinde kullanılır. 
Sıvı ham demirde silisyum içeriği ne kadar yüksekse, bu yüksek miktardaki silisyumun yanması sırasında ortaya çıkan enerjiyi kompanse edebilmek için o oranda hurda kullanımı artış göstermektedir. Çelik üretiminde hurda kullanımı belirli bir oranın üzerinde olduğunda üretim maliyetinin artması, proseste yaşanan zorluklar ve verim kaybı nedeniyle tercih edilmez. Hurda fiyatları spekülatif fiyat hareketlerinin olduğu dönemler hariç sıvı ham demir maliyetlerinin üzerinde seyretmektedir. Sıvı ham demir içerisindeki fazla silisyum konvertör prosesinde silisyum dioksite dönüşürken, hedeflenen bazitenin tutturulabilmesi için daha fazla kalsiyum oksit ilavesi gerektirir. Oluşan fazla cüruf taşmalara neden olur. Bunun sonucu olarak ısı ve metal kayıpları yaşanmaktadır. Hurda kullanımı artışına bağlı olarak empürite elementlerin sürece girişinin kontrolü zorlaşmaktadır. Bu da hedeflenen çelik kalitelerinin kontrolünü zorlaştırmaktadır. Dolayısı ile sıvı ham demir içerisindeki silisyumun miktarının kontrol edilmesi, istikrarlı, verimli ve kaliteli bir çelik üretim süreci için önemlidir.
Silisyum, yüksek fırına şarj malzemeleri ile silisyum dioksit formunda girmektedir. İndirgeyici ortam koşullarında bir bölümü indirgenerek silisyum halinde dönüşür ve sıvı ham demire geçer. Yüksek fırın ısıl durumuna göre metal ve cüruf fazlarına geçişi değişim gösterir. Isıl durum potansiyeli arttıkça sıvı ham demir içerindeki silisyum miktarı da artış göstermektedir. Yüksek fırın prosesi kaynaklı bu tür dalgalanmalar oluştuğunda istikrarlı çelik üretim prosesi de bu dalgalanmalardan olumsuz etkilenmektedir.
Sıvı ham demir içerisindeki silisyumun yüksek fırın prosesinde minimize edilmesinin sınırlı olması sebebiyle ön işlem yoluyla azaltılmasına yönelik çalışmalar gerçekleştirilmiştir. Yüksek fırın döküm kanallarında, yüksek fırın ve çelikhane arasındaki bir istasyonda silisyumun düşürülmesi sağlanabilmektedir. 
Bu çalışmada sıvı ham demir içerisindeki silisyum miktarının azaltılmasına yönelik için, yüksek fırın döküm kanallarına demir oksit kaynağı olarak kullanılan tufalın ilavesi gerçekleştirilmiştir. İlave dilen tufal miktarına bağlı olarak alınan numunelerdeki silisyumun azaltılma oranı incelenmiştir. Deneysel çalışmalar sonucunda sıvı ham demire ilave edilen tufal miktarının artırılmasına paralel olarak silisyum miktarında artan oranda azalma olduğu görülmektedir.

Abstract:
In integrated steel plants, hot metal produced in blast furnaces should be suitable for steel workshops such as chemical analysis and temperature. In steel production, impurities such as silicon, manganese, sulfur, phosphorus and carbon must be removed. Sulfur content is minimized in the blast furnace to the point where the blast furnace production performance is adversely affected. The rest of sulfur is eliminated in pre-treatment process before steel production in an intermediate desulfurization plant. Silicon, manganese, phosphorus and carbon are oxidized by pure oxygen in the BOF process, which is produced steel. These oxidized elements pass through the BOF slag and are removed from the produced steel.
Silicon in hot metal is one of the important elements for steel production. In the steel shop, a high percentage of silicon is converted to silicon oxide using pure oxygen in the BOF process. These combustion reactions result in high heat energy, which causes the overheating of the liquid metal bath. In order to control this excess heat, the scrap is added to hot metal in BOF process. In today's steel production process, chemical analysis and temperature of hot metal produced in blast furnace are transferred to computer models of BOF convertor. These information is entered as data set, mostly transferred automatically via network from lab to computer models of BOF. The combustion reactions caused by the blowing of pure oxygen in the converter are evaluated according to thermodynamic and kinetic principles. Process simulation is performed by processing with mathematical process models based on these principles. These models perform mass and heat balance calculations considering weights, analysis, temperatures of all inputs. In particular, the rate of scrap that can be charged to the BOF convertor due to the content of hot metal silicon is calculated in this way. First, the calculated amount of scrap is charged in to the convertor, then the hot metal is charged. After this step, operation of conversion hot metal to steel is starts with blowing pure oxygen. The target steel temperature and quality are based on the initial model calculations and the duration of the oxygen blowing and related parameters.
As a result of the increase of silicon content of hot metal in the blast furnace production, the energy generated during combustion of silicon oxidized in the converter process is also increasing. The rate of scrap usage in the converter needs to be increased in order to tolerate this excess energy. This means that in steel production, more scrap is used instead of hot metal because of converter has a certain volume and capacity. 
The increase in the use of scrap in steel production is not preferred due to increase in the cost of production, the operational difficulties that may be experienced and the losses in production efficiency.
When the hot metal silicone content increases, it is not preferable to increase the use of scrap in the BOF process instead of the hot metal which is cheap in the converter. Scrap prices are generally above the cost of hot metal produced in the blast furnace, except for periods with speculative price movements. This means higher cost of steel production as scrap utilization increases for integrated plants.
In the BOF converter, the usage of scrap of which chemical analysis is limited instead of hot metal which chemical analysis are regularly done, causes more chemical analysis deviation in steel composition.
Due to the high amount of silicon in the hot metal, some problems occurs in terms of BOF slag in the converter for steel production. The excess silicon in the hot metal requires more calcium oxide to achieve the target basicity in the BOF process. The accumulation of silicon dioxide from the oxidized silicon leads to converter overflows which is caused by the addition of extra calcium oxide added, to achieve the target basicity of slag. For this reason, the control of silicon in hot metal is important for a stable, efficient and high-quality steel production process. In particular, the increase in the value of silicon is not desirable due to the problems mentioned above in the BOF process in which steel production is carried out.
Silicon which is the form of silicon dioxide enters from the top of the blast furnace as a part of raw material. A portion of the silicon dioxide is reduced in the blast furnace process conditions and pass into hot metal in the form of silicon. The transition to the metal and slag phases depends on the thermal condition of the blast furnace. Hot metal silicon content increases the potential of blast furnace heat. When such fluctuations occur in the blast furnace process, the stabilization of the steel production process is adversely affected by the mentioned problems.
The control of hot metal silicon content in the blast furnace process depends on many different parameters. While blast furnace operators try to produce hot metal with the desired chemical analysis by the steel shop, they also have to manage elements such as alkaline, zinc and alumina which cause problems in the blast furnace process stabilization. This is adversely affect maximize hot metal production. Raw material quality fluctuations make it difficult to be kept the hot metal temperature and chemical analysis stable. Optimization of all these difficulties leads to the reduction of silicon dioxide in the blast furnace at a certain rate. Fluctuations due to the quality of the fuel-based raw materials in particular can change the thermal state of the blast furnace. In this case, which is reflected by the increase in hot metal temperature, more silicon means passed to hot metal.
Due to limitations in blast furnace process conditions, some work has been done to reduce the hot metal silicon content by applying pre-converter pretreatment methods. In different applications, methods have been developed in which the hot metal silicone content is removed in blast furnace castings or hot metal transport (torpedo, ladle) vehicles. Particularly Japanese steel producers have applied pre-treatment methods of silicon removal and further dephosphorization together with hot metal desulfurization pretreatment methods which are widely used in the integrated steel companies.
Hot metal silicon content is reduced by adding iron oxide based materials to hot liquid metal in blast furnace runners. Silicon oxide is one of most stable earth oxide. Silicon' oxygen interest is higher than iron' oxygen interest. When the iron oxide is added into the hot metal, oxygen potential occurs. Therefore silicon is converted to silicon dioxide and iron loses its oxygen, melts into the hot metal. In integrated steel plants, sinter fines, ore fines, iron-bearing raw material's dust which cannot be used in other process and rolling scale are used for reducing the hot metal silicon content.
In this study, in order to reduce the amount of silicon in the hot metal, rolling mill scale as iron oxide source is used additionally in the blast furnace runners. The reduction rate of silicon was investigated depending on the amount of addition scale. Experimental studies have shown that the content of hot metal silicon decreases as the amount of added scale increases. It has been calculated that the proportion of scrap used in the BOF process is reduced due to the reducing of silicon content in hot metal.
It has been assessed that hot metal silicon content can be reduced with a low investment cost with the usage of iron oxide sources which is waste in blast furnace casthouse runners and hot metal torpedo transport vehicles therefore scrap usage ratio in BOF process is decreased.