Understanding Steel Making Operations  in Basic Oxygen Furnace Mar02

Understanding Steel Making Operations in Basic Oxygen Furnace...

Understanding Steel Making Operations  in Basic Oxygen Furnace  Steel making operation in the basic oxygen furnace (BOF) is also sometimes called basic oxygen steel making (BOS). This is the most powerful and effective steel making technology in the world. Around 71 % of the crude steel is made by this process. BOF process was developed in Austria in the early 1950s at the two Austrian steelworks at Linz and Donawitz and hence the BOF process is also called LD (first letters of the two cities) steel making. There exist several variations on the BOF process. The main are top blowing, bottom blowing, and a combination of the two which is known as combined blowing. The BOF process is autogenous, or self sufficient in energy, converts liquid iron (hot metal) into steel using gaseous oxygen (O2) to oxidize the unwanted impurities in hot metal (HM). The O2 used must be of high purity, usually 99.5% minimum, otherwise the steel may absorb harmful nitrogen (N2). The primary raw materials for the BOF are generally HM (around 80 % or more) from the blast furnace and the remaining steel scrap. These are charged into the BOF vessel. O2 is blown into the BOF at supersonic velocities. It oxidizes the carbon (C) and silicon (Si) contained in the HM liberating great quantities of heat which melts the scrap. There are lesser energy contributions from the oxidation of iron(Fe), manganese (Mn), and phosphorus (P). The flux used in this process is primarily calcined lime ( with CaO content of more than 92 %). This lime is produced by the calcining of limestone with low silica (SiO2) content. The post combustion of carbon monoxide (CO) as it exits the converter also transmits heat back to the bath. The product of...

Lime and Calcined Dolomite for Use in Steel Plant...

Lime and Calcined Dolomite for Use in Steel Plant Lime is a versatile compound.  Various forms of lime are used in environmental, metallurgical, construction, and chemical/industrial applications etc.  The largest single use of lime is in steel manufacturing, where it serves as a  flux for removing impurities (silica, phosphorus, and sulphur) during refining of steel. The fastest growing use of lime is in environmental applications, where lime is used for treatment of flue gases, wastewater, solid waste, and drinking water. Lime is a white crystalline solid with a melting point of 2572 deg C. It is a basic oxide and is used to react with the acidic oxides (e.g. silica) in various smelting operations. With water it makes milk of lime used for neutralizing acidic waste water. It is also being known as quick lime, lime flux, unslaked lime, and fluxing lime. Lime having some percentage of MgO (usually 2 % to 4 %) is also known as dolomitic lime. Lime is a hygroscopic material and absorbs moisture from the air. With the absorption of moisture it loses its reactivity and gets hydrated. Lime is calcium oxide (CaO) produced on heating (calcination) of limestone (CaCO3) to a temperature of 900 deg C and above (usually 1100 deg C). CaCO3(s) + heat = CaO(s)  +CO2(g) This reaction is reversible. Calcium oxide reacts with carbon dioxide to form calcium carbonate. The reaction is driven to the right by flushing of carbon dioxide from the mixture as it is released. Hydrated lime [Ca(OH)2] is formed by reaction of lime with water (slaking). CaO + H2O = Ca(OH)2 + heat Hydrated lime is also known as slaked lime. It is in the form of a dry white powder. Hydrated lime is an alkali and used for neutralizing acidic solutions. In...

Steel Scrap

Steel Scrap Steel scrap consists of discarded steel or steel products, generally segregated by composition and size or ‘grade’ suitable for melting. There are three main types of scrap which are used by the steel industry as feed stock. These are (i) internal scrap, (ii) prompt scrap, and (iii) obsolete scrap. Internal scrap is also known as revert or home scrap. It refers to the reject metal within the steel plant which gets generated during steel making, steel casting and steel finishing activities within the steel plant. Prompt scrap is also known as process scrap and it is the waste generated during the product manufacturing by the steel plant’s customers i.e. the manufacturing industries. Obsolete scrap consists of that scrap which is recovered from discarded industrial and consumer items i.e. from ships to refrigerators and from construction beams to automobiles. The first two categories of scrap can be returned to the steel making process with little or no pretreatment, obsolete scrap needs to be separated from contaminants, sorted and prepared for steel making. Due to the large improvements which have taken place in the steel manufacturing, steel casting, steel finishing, and product manufacturing technologies in the recent past, the amount of generation of the first two types of scraps have reduced a lot. On the other hand with resources of obsolete scrap are increasing as the world is becoming more industrialized and due to larger quantity of discarded consumer durables and worn out industrial equipment etc. Another way of classifying steel scrap is to classify it according to the products in which the steel was used before it became scrap. The main steel scrap sources in this sense are automobiles, ships, railroads, construction buildings, machinery, white goods, packaging, electric and electronic equipment etc. Steel...

Steelmaking by Induction Furnace Mar26

Steelmaking by Induction Furnace...

Steel making by Induction Furnace Though induction furnaces are being used since a long time, the production of mild steel by the induction furnace (IF) is relatively a very recent phenomenon. Induction furnaces work on the principle of electromagnetic induction which was discovered by Michael Faraday. History In 1870 De Ferranti started experiments in Europe on induction furnaces. The first induction furnace for melting metals was patented by Edward Allen Colby in 1900. The first steel made in an induction furnace in United States was in 1907 in a Colby furnace near Philadelphia. First 3 phase furnace was built in Germany in 1906 by Rochling- Rodenhauser. In India the use of induction furnaces started in mid sixties. Imported medium frequency induction furnaces were used from mid seventies. Early eighties to mid nineties sudden growth has taken place. During this period indigenous manufacture of the induction furnaces also started. Initially induction furnaces were used for melting stainless steel scrap but these furnaces are used for mild steel production from mid eighties. Characteristics of Induction furnace There are mainly two types of the induction furnaces. They are given below. i) Induction channel furnace – In this furnace induction heating takes place in the channel which is a small and narrow area at the bottom of the main bath. The channel passes through a steel core and the coil assembly. Such type of furnaces are not been used for the steel making. ii) Induction crucible furnace- This type of the furnace is also called coreless induction furnace. It is a refractory lined vessel (Crucible). Its other main components are power supply unit consisting of transformer, inverter and capacitor bank, the charging arrangement, the cooling system for the power supply and furnace coil, process control system and the...

Role of MgO in prevention of lining corrosion in converters Mar06

Role of MgO in prevention of lining corrosion in converters...

        Role of MgO in prevention of lining corrosion in converters In the present day primary steelmaking processes, magnesia carbon bricks are the most commonly used refractory material for lining of the primary steel making furnace. The lining life differs from steel plant to steel plant because of refractory, operation and maintenance practices (Fig. 1). Fig 1 Effects of various refractory wear factors The effect of different parameters on the lining life is elaborated in Table 1 Table 1 Effects of different parameters on lining life Sl.No. Parameter Effect on life Severity of influence 1 Hot Metal Si Negative Medium Mn Positive Low Ti Negative Low 2 Slag Total Fe Content Negative High Basicity(CaO/SiO2) Positive Medium CaF2 Addition Negative Medium MgO content Positive High Al2O3 Content Negative Low Lime Addition Positive Medium 3 Blowing End point Temperature Negative High Blowing duration Negative Medium Production rate (Heats/day) Positive Medium Slag Volume Negative Low Atmosphere (CO/CO2) Positive Medium Delay in charging lime Negative Medium 4 Design of Converter Vessel volume Positive Low Cone angle Positive Low Multi hole blow lance Positive high The relationship of some of the parameters influencing the lining life of the converter is shown in Figure 2.   Fig 2 Relationship of the parameters affecting the lining life During the process of steel making, the main wear mechanisms are impact, corrosion, thermo-mechanical stresses and erosion. Though all the factors are important but corrosion due to dissolution of refractory material in the slag has a major effect on the lining life. During the process of steel making various oxides are produced which are fluxed with calcined lime to produce steel making slag. This slag is corrosive in nature and is in continuous touch with the surface of the converter lining. Due...