Importance of Hearth, Dead man and Tapping in Blast Furnace Operation Apr13

Importance of Hearth, Dead man and Tapping in Blast Furnace Operation...

Importance of Hearth, Dead man and Tapping in Blast Furnace Operation  A trend of deterioration in ore quality is seen these days with the increasing demand for iron ore. The deterioration in ore quality is accompanied with higher quantities of slag which in turn affects burden descent and liquid flow through the hearth. These conditions provide a catalyst for lining wear mechanism with bosh, stack and hearth linings coming under additional stress. Tapping in the blast furnace is adversely affected and trough and runners in the cast house get under strain due to higher slag volume. All these put increased pressure on blast furnace operations. The poor quality of iron ore affects the operation of the blast furnace in the following way. Slag volume – Poor quality of iron ores bring into the furnace higher quantities of impurities resulting into increase in the slag volumes. Heat load – The furnace thermal condition undergoes changes since a large quantity of heat is required to melt the additional slag as well as to keep it in proper fluid state for its drainage. This introduces higher heat loads inside the blast furnace. Coke rate and productivity – Increasing slag volumes needs a higher fuel input into the furnace, and where pulverized coal injection rates are already running at optimum, this results into a higher coke rate. Higher coke means introduction of higher amount of ash in the furnace resulting into further increase in the slag volume. This has got a deteriorating effect on the productivity of the furnace. Process stability – The deterioration in the ore quality affects the process stability adversely and has an unfavourable effect on the smooth running of the blast furnace. Due to the above factors, the production process in the blast furnace...

Handling of Hot Metal in Blast Furnace Iron Making Feb10

Handling of Hot Metal in Blast Furnace Iron Making...

Handling of Hot Metal in Blast Furnace Iron Making  Hot metal (HM) is produced by the reduction of descending ore burden by the ascending reducing gases in a blast furnace (BF). It is liquid in nature and gets collected in the hearth of the BF. From the hearth, the HM is tapped from the taphole of the BF after an interval of time. Normally in large BFs, HM tapping rates of 7 ton/min and liquid tapping velocities of 5 m/sec, in tap holes of 70 mm diameter and 3.5 m long, are typically encountered. The tapping rate of HM is strongly influenced by the taphole condition and taphole length. Generally the temperature of tapped HM varies in the range of 1420 deg C to 1480 deg C. The tapped HM is handled in the following three stages. Handling of the HM in the cast house i.e. from taphole to the hot metal ladles HM ladles and their transport Processing of HM either in the pig casting machine (PCM) for the production of pig iron (PI) or in the steel melting shop for making steel. Historical development of hot metal handling During the seventeenth century, the produced liquid iron (usually around 450 kg per cast) from the iron making furnace was drawn into a single trench or ladled into sand moulds to produce domestic products such as pots, pans, stove plates etc.  As the BF production increased due to many design improvements, removal of liquid products (iron and slag) became an issue. Production of charcoal BF had increased over the period from one ton to 25 tons per day. This higher tonnage could not be handled with two casts per day through a single trench in front of the tap hole. The cast house contained...

Quality of Lime for Steelmaking in Converter Sep08

Quality of Lime for Steelmaking in Converter...

Quality of Lime for Steelmaking in Converter 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). It 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). Hydrated lime is also known as slaked lime. CaO + H2O = Ca(OH)2 + heat Lime as a basic flux in steel production and it plays an important role in the sequence of metallurgical reactions taking place in a converter. Steel is produced from hot metal by oxidizing sulphur (S), phosphorus (P), carbon (C), silicon (Si), manganese (Mn), and other impurities so that they can enter the slag or gas phases, thus separating from the metal phase. Lime in steelmaking is mainly used to produce slag for the removal of these harmful elements in liquid bath and optimize the quality of liquid steel. The basic oxygen process oxidizes impurities in an oxygen converter also known as basic oxygen furnace (BOF) where the hot metal comes in contact with oxygen. Oxidized impurities of the hot metal are absorbed in a slag, which is formed with the help of calcined lime. Metallurgical lime in the fifties consisted of a mixture of particles of all sizes from very coarse to very fine, with additional components such as silicon dioxide and sulphur concentrated...

Slag and its Role in Blast Furnace Ironmaking Aug07

Slag and its Role in Blast Furnace Ironmaking...

Slag and its Role in Blast Furnace Ironmaking Blast furnace (BF) is the oldest (more than 700 years old) of the various reactors which are being used in the steel plants. It is used for the production of liquid iron (hot metal). The blast furnace is a complex high temperature counter current reactor and is in the shape of a shaft in which iron bearing materials (ore, sinter/pellet) and coke are alternately charged at the top along with flux materials (limestone, dolomite etc.) to create a layered burden in the furnace. Preheated air is blown in from the lower part of the furnace through tuyeres. This hot air reacts with the coke to produce reducing gases. Descending ore burden (iron oxides) is reduced by the ascending reducing gases and is melted to produce hot metal. The gangue materials and coke ash melt to form slag with the fluxing materials. The liquid products (hot metal and slag) are drained out (tapped) from the furnace at certain intervals through the tap hole. The quality of hot metal obtained is dependent on the formation of the slag and its mineralogical transformations. A good quality slag is necessary for a quality hot metal. The slag is a mixture of low melting chemical compounds formed by the chemical reaction of the gangue of the iron bearing burden and coke ash with the flux materials in the charge. All unreduced compounds such as silicates, aluminosilicates, and calcium alumino silicate etc. also join the slag. It is well known that the components of slag namely silica (SiO2) and alumina (Al2O3) increase the viscosity whereas the presence of calcium oxide reduces the viscosity. The melting zone of slag determines the cohesive zone of blast furnace and hence the fluidity and melting characteristics...

Role of Slag in Converter Steelmaking Aug01

Role of Slag in Converter Steelmaking...

Role of Slag in Converter Steelmaking The oxygen converter process is the primary steelmaking process for the production of carbon and low-alloy steels. The process is essentially an oxidizing process of refining of the high carbon hot metal (HM) to low carbon liquid steel. The oxidizing process is carried out by blowing oxygen in the converter. This causes liquid iron and the other metallic and non-metallic impurities present in the liquid melt in the converter bath to form oxides that are lighter than the liquid steel and they float to the surface of the bath. The generic name of these oxides is ‘slag’. Some oxides are acidic in nature which can react with the basic refractories of the converter and hence a basic slag using lime and calcined dolomite is usually made for protecting the converter refractories. The oxygen can also react with carbon to create a gas that provides bubbles for foaming the liquid slag and for providing chemical energy needed during steelmaking. In steelmaking process, the slag is predominantly a mixture of oxides with small amounts of sulphides and phosphides. The oxides are either acidic or basic in nature. Slag is formed during refining of hot metal in which Si oxidizes to SiO2, Mn to MnO, Fe to FeO, and P to P2O5 etc., and addition of oxides such as CaO (lime), MgO (calcined dolomite), iron oxide, and others. The addition of oxides is done to obtain desired physico-chemical properties of slag like melting point, basicity, viscosity etc. There are four primary sources for the slag during the steelmaking process in the converter. These are (i) oxidation of metallic elements in the liquid steel (e.g. silicon, manganese, aluminum, titanium, chromium, and vanadium etc.), (ii) due to presence of non-metallics in the liquid...