Hydrogen gas and its use in Iron and Steel industry...

Hydrogen gas and its use in Iron and Steel industry Hydrogen is a chemical element, ranking first in the periodic table with element symbol of ‘H’. The (atomic number of hydrogen element is 1 and atomic weight is 1.008. It is the smallest atom in the universe and the simplest element in nature. Its molecule consists of two hydrogen atoms. It is the lightest gas, being about 1/14 times as dense as air. It has three isotopes named (i) protium, (ii) deuterium, and (iii) tritium. Pure hydrogen is odourless, colourless and tasteless. Hydrogen has lowest atomic weight of any substance and therefore has very low density both as a gas and a liquid. The vapour density of hydrogen at 20 deg C and 1 atmosphere pressure is 0.08376 kg/cum. The specific gravity of gaseous hydrogen is 0.0696 and hence, it has around 7 % the density of air. The density of liquid hydrogen at normal boiling point and 1 atmosphere pressure is 70.8 kg/cum. The specific gravity of liquid hydrogen is 0.0708 and is thus, it has around 7 % the density of water. Hydrogen is a liquid below its boiling point of -253 deg C and a solid below its melting point of – 259 deg C at atmospheric pressure. It is non-toxic but can act as a simple asphyxiant by displacing the oxygen in the air. When hydrogen is stored as a high-pressure gas at 250 kg/cum and atmospheric temperature, its expansion ratio to atmospheric pressure is 1:240. The molecules of hydrogen gas are smaller than all other gases, and it can diffuse through many materials considered airtight or impermeable to other gases. This property makes hydrogen more difficult to contain than other gases. Leaks of liquid hydrogen evaporate very quickly since the...

Coal Tar Pitch

Coal Tar Pitch  Coal tar pitch, derived from by-product coke ovens, is the preferred material for use as a binder in the manufacture of carbon and graphite electrodes. Coal tar pitch is a coal conversion product. Its IUPAC name is ‘Coal Tar Pitch, High temperature”. Its CAS number is 65996-32-2 and EINECS number is 266-028-2. It is the shiny, dark-brown to black residue produced by distillation of coal tar. Coal tar pitch contains a large number of substances. It is solid at room temperature and consists of a complex mixture of numerous polycyclic aromatic hydrocarbons (PAHs), their methyl and polymethyl derivatives, and heterocyclics, and shows a broad softening range instead of a defined melting temperature. The hydrogen (H2) aromaticity of coal tar pitch (ratio of aromatic to total content of H2 atoms) varies from 0.7 to 0.9. Production of coal tar pitch Coal tar pitch is currently produced from coal tar, which is a byproduct of high temperature coking of coal in the manufacture of metallurgical coke. The tar predominantly contains a mixture of bi- and poly-condensed aromatic hydrocarbons and also compounds with heteroatoms in rings (predominantly nitrogen bases from the quinoline and acridine series, 1 % to 2 %) and phenols (1 % to 2 %). Upon distillation, 8 % to 12 % of a naphthalene fraction, 5 % to 9 % of an absorption fraction, and 21 % to 26 % of an anthracene fraction, which boiled away to 360 deg ?, are separated. The residual part of the tar is the pitch which contains nonvolatile and low volatile substances, whose average yield is around 2 % of the coking coal charge used for high temperature carbonizing. The industrial production of coal tar pitch consists of the fractional distillation of the coal...

Coal Ash

Coal Ash Coal ash is the mineral matter present in the coal. It is a waste which is left after coal is combusted (burned). It is the particulate material which remains after coal is burned. It includes fly ash (fine powdery particles which are carried up the smoke stack and captured by pollution control devices) as well as coarser materials which fall to the bottom of the furnace. It has different physical and chemical properties depending on the geochemical properties of the coal being used and how that coal is burned. Coal ash is also referred to as coal combustion residuals. It has very little organic fraction. Chemical constituents of coal ash may include nitrogen (N2), sulphur (S), unburned carbon (C), heavy metals, radioactive elements, and polycyclic aromatic hydrocarbons (PAHs). Coal ash also contains coarse particles and fine particles which can be inhaled and may contribute to public health and environmental problems. Coal ash contains many toxic contaminants. When coal ash spills, leaks or leaches into nearby ground water or waterways, the toxins contained within pose serious health risks to nearby communities. Depending on where the coal was mined, coal ash typically contains heavy metals including arsenic, lead, mercury, cadmium, chromium and selenium, as well as aluminum, antimony, barium, beryllium, boron, chlorine, cobalt, manganese, molybdenum, nickel, thallium, vanadium, and zinc. If eaten, drunk or inhaled, these toxicants can cause cancer and nervous system impacts such as cognitive deficits, developmental delays and behavioral problems. They can also cause heart damage, lung disease, respiratory distress, kidney disease, reproductive problems, gastrointestinal illness, birth defects, and impaired bone growth in children. A large amount of coal ash is disposed in dry landfills, frequently at the power plant where the coal was burned. Coal can also be mixed with...

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...