Properties and Structure of Metallurgical Coke...

Properties and Structure of Metallurgical Coke Metallurgical coke is a porous, fissured, silver-black solid and is an important part of the ironmaking process since it provides the carbon (C) and heat required to chemically reduce iron burden in the blast furnace (BF) to produce hot metal (HM). It is a porous C material with high strength produced by carbonization of coals of specific rank or of coal blends at temperatures around 1100 deg C in coke ovens. It is composed of both the organic and inorganic matter. C is the major component of the organic part. Small amounts of sulphur (S), nitrogen (N2), hydrogen (H2) and oxygen (O2) also occur in the organic part. The inorganic matter in coke is called coke ash (mineral matter) and is typically around 12 % on dry basis. Both the organic and inorganic components influence coke reactivity. Thus, coke characterization is an important aspect to understand the quality of coke formed. The basic understanding of coke quality is an important task as it determines the high temperature and gasification behaviours of coke in the blast furnace (BF). As the coke moves towards the lower zones of BF, it degrades and generates fines, which affects the bed permeability and the process efficiency. Hence, superior coke quality is critical for a stable and efficient BF operation. Coke quality is influenced by many factors such as the rank, the maceral composition (leading to isotropic or anisotropic coke structures), the ash composition and the fluidity of the starting coals, the carbonization conditions including peak temperature, heating rate, particle size, pressure and bulk density as well as heat treatment conditions. The important properties of coke, including mechanical strength and reactivity, are governed by the arrangement of the constituent C atoms. The principal features...

Properties and Uses of Ironmaking slag...

Properties and Uses of Ironmaking slag The majority of iron in the world is produced in the blast furnace (BF) and hence BF slag represents the largest quantity of ironmaking slag produced around the world. The BF is the primary means for reducing iron (Fe) oxides to molten, metallic iron. It is continuously charged with Fe oxide sources (ore, sinter, and pellet etc.), fluxes (limestone, and dolomite), and fuel (coke, and coal). Liquid iron collects in the bottom of the furnace and the liquid slag floats on it. Both are periodically tapped from the furnace. BF slag is defined by the American Society for Testing and Materials (ASTM). It defines BF slag as the non-metallic product consisting essentially of silicates and alumino-silicates of calcium and other bases which is developed in a molten condition simultaneously with iron in a BF. The slag consists primarily of the impurities from the iron ore, mainly silica (SiO2) and alumina (Al2O3), combined with calcium (Ca) and magnesium (Mg) oxides from the fluxes. Sulphur (S) and ash which normally come from coke and coal are also contained in the slag. Slag comes from the furnace as a liquid at temperatures of around 1500 deg C. It is a man-made molten rock, similar in many respects to volcanic lavas. Chemical and mineralogical composition of BF slag Chemical analysis of BF slag normally consists of four major oxides namely (i) SiO2, (ii) Al2O3, (iii) calcium oxide (CaO), and (iv) magnesia (MgO). These oxides make up around 95 % of the total quantity. Minor elements which are present in the slag are Fe, S, manganese (Mn), alkalis, and trace amounts of several other elements. Common composition range of various components of BF slag is given in Tab 1. Tab 1 Range of...

Properties and Uses of Steelmaking Slag...

Properties and Uses of Steelmaking Slag Steelmaking slag is an integral part of the steelmaking process. It is produced during the separation of the liquid steel from impurities in steelmaking furnace and is a non-metallic by-product of steelmaking process. It occurs as a molten liquid melt and is a complex solution of silicates and oxides which solidifies upon cooling. It primarily consists of silicates, alumina silicates, calcium aluminum silicates, iron oxides and crystalline compounds. During steelmaking, slag is produced in the hot metal pretreatment processes (desulphurization, desiliconization, and dephosphorization etc.), in the primary steelmaking processes (basic oxygen furnace, electric arc furnace, and induction furnace), slag formed during the secondary refining processes (this slag is sometimes called ?secondary refining slag? or ?ladle slag?), and slag formed in tundish during continuous casting of steel (also known as tundish slag). The slag generated in the basic oxygen furnace (BOF) and electric arc furnace (EAF) is of basic nature while the slag is of acidic nature in induction furnace because of the use of silica ramming mass as the lining material. Since most of the steel produced in the world is by BOF and EAF processes, hence slag from these processes is discussed in this article. The processing of the steelmaking slag (Fig 1) is normally carried out by (i) solidifying and cooling of the hot liquid slag, (ii) crushing and magnetic separation treatment of the slag to recover the scrap, (iii) crushing and classification of the slag for grain size adjustment to manufacture the slag product, and (iv) aging treatment of the slag product for improving its quality and volumetric stability. These processes are explained below.   Fig 1 Processing of steelmaking slag As steelmaking slag is formed, it is in a molten or red-hot state at...

Hot Metal

Hot Metal Hot metal (HM) is the output of a blast furnace (BF). It is liquid iron which is produced by the reduction of descending ore burden (iron ore lump, sinter, and pellet) by the ascending reducing gases. HM 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 two stages namely (i) handling of the HM in the cast house i.e. from taphole to the hot metal ladles (open top or torpedo), and (ii) transport of HM ladles to the point of HM consumption. Presently most of the HM is consumed within integrated steel plants for steel making. The HM is transferred to the steel melting shop for making of steel. The HM which is not sent for steel making is cast into pig iron in pig casting machine for use in steel making later as cold charge or is sold to foundries or to mini steel plants having induction furnaces as merchant pig iron. HM can also be granulated by a process which is known as ‘Granshot’ process. Presently the Granshot plants for the production of GPI are working at six places namely (i) Uddeholm, Sweden, (ii) SSAB Lulea, Sweden, (iii) Voest Alpine, Donawitz, (iv) Saldanha steel, South Africa, (v) SSAB Oxelosund, Sweden, and (vi)...

Natural gas and its Usage in Iron and Steel Industry...

Natural gas and its Usage in Iron and Steel Industry Natural gas (NG) is an environmentally friendly non-renewable gaseous fossil fuel which is extracted from deposits in the earth. It is a clean and green fuel with a high efficiency and plays a major role in helping many industries cut emissions and improve the overall air quality. It is normally supplied as (i) piped natural gas (PNG), (ii) compressed natural gas (CNG), and (iii) liquefied natural gas (LNG). Natural gas is a mixture of hydro-carbons consisting primarily of methane (CH4), generally in a percentage of over 85 % by volume. Other hydro-carbons in NG include varying amounts of various higher alkanes such as ethane, propane, and butane etc. It also contains water vapour (H2O) at varying degrees of saturation, or condensed water. It may also contain some small percentage of nitrogen (N2), carbon dioxide (CO2) and hydrogen sulphide (H2S) and helium (He) etc. NG burns with a clean blue luminous flame when mixed with the requisite amount of air and ignited. It is considered one of the cleanest burning fuels. On burning, it produces primarily heat, CO2, and water vapour. NG is a fuel found in deposits in its gas phase. It is colourless and odourless, non-toxic, and lighter than air. It does not contain olefins (hydrocarbons produced during the process of destructive distillation or reforming). It is a highly flammable and combustible gas. Its CAS number is 8006-14-2 and UN number is 1971. Quantities of natural gas are measured in normal cubic meters (corresponding to 0 deg C and 1 atmosphere pressure) or standard cubic feet (corresponding to 16 deg C and 14.73 pounds per square inch absolute pressure). The higher heat value of one cubic meter of natural gas varies from around 9500...

Thermal Coal

Thermal Coal Thermal coal is a type of bituminous coal which is used to provide heat energy in combustion in various types of furnaces via the pulverized fuel method because of its high calorific value (CV). It is also sometimes called as non-coking coal, steam coal, or boiler coal. It includes all those bituminous coals which are not included under coking coal category. It is characterized by higher volatile matter (VM) than anthracite (more than 10 %) and lower carbon (C) content (less than 90 % fixed C). Its gross CV is greater than 5700 kcal/kg on an ash?free but moist basis. The greatest use of thermal coal is for the generation of steam in the boilers for the purpose of generation of electricity. Thermal coal is also used in some of the processes for ironmaking especially in the production of direct reduced iron (DRI) and in the smelting reduction processes for the production of hot metal (HM). Thermal coal is a complex heterogeneous substance. Hence, it has no fixed chemical formula. Its characteristics and hence its CV vary widely. Thermal coals like other coals also contain carbon (C), oxygen (O2), and hydrogen (H2). The other constituents in thermal coals include sulphur (S), nitrogen (N2), ash, chlorine (Cl), and sodium (Na). The quality of thermal of coals is based on the amount of C, O2, and H2 present in coal. The metallic elements in the thermal coal contribute to the coal ash. The chemical structure of the organic molecules of the thermal coal is very complex and is dependent on the rank of the coal. It varies from one coal to another coal. Typical structure of thermal coal is given in Fig 1. Fig 1 Typical structure of thermal coal The performance of the...