Bituminous coal

Bituminous coal Bituminous coal is an organic sedimentary rock formed by diagenetic and sub metamorphic compression of peat bog material. It is also called as black coal. It is often referred to as soft coal. However, this designation is a layman’s term and has little to do with the hardness of the rock. Bituminous coal is by far the largest group and is characterized as having lower fixed carbon (C) and higher volatile matter than anthracite coals. It is the type of coal which is most widely used in the world today. Bituminous coal is the second highest quality of coal (below anthracite) and the most abundant type. Usually, bituminous coal comes from fairly old coal deposits (around 300 million years old).The energy density of this coal is relatively high, therefore, releases a significant amount of energy when burned. Bituminous coal is defined as a medium?rank coal with either a gross calorific value (CV) on a moist, ash?free basis of not less than 24 mega joules per kilogram (MJ/kg) and with a Vitrinite mean Random Reflectance less than 2.0 %, or with a gross CV on a moist, ash?free basis of less than 24 MJ/kg provided that the Vitrinite mean random reflectance is equal to, or greater than 0.6 %. Bituminous coals are agglomerating and have a higher volatile matter (VM) and lower C content than anthracite coal. This coal is originated by coalification of plant matter deposited in sequences dominated by clastic sediments under diagenetic conditions (thermal and pressure mode) of a given coal basin. Coalification proceeded under geologic time scale. In various coal basins (coal seams) coal matter differs in regard of different primary composition of plant matter and sedimentary environment. Composition of coal (e.g. elemental composition, VM etc.) and mean reflectance of vitrinite reflect final stage of coal metamorphism of a given sedimentary basin. Bituminous...

Anthracite Coal

Anthracite Coal Anthracite coal derives its name from the Greek word ‘anthrakít?s’, literally meaning ‘coal-like’.  It is frequently being referred as hard coal and is one of the four types of coals. Other types of coals are lignite coal, sub- bituminous coal and bituminous coal. Since anthracite coal had been subjected to the intense pressure and heat, it is the most compressed and hardest coal available. Being a hard coal, it contains greater potential to produce heat energy than softer, geologically ‘newer’ coal. As per ISO 11760:2005, anthracite coal is defined as the coal, synonymous with high-rank coal, having a mean random vitrinite reflectance, equal to or greater than 2.0 % but less than 6.0 %, or, preferably, a mean maximum reflectance, , less than 8.0 % for geologically unaltered coal. Geology and mining of anthracite coal Anthracite coal was formed from bituminous coal when great pressures had developed in the folded rock. Transformation of the bituminous coal into anthracite is called ‘Anthracitization’. It was formed during the Carboniferous Age, when the dense green vegetation that thrived during the tropical climate of the time fossilized. It is the oldest and cleanest type of coal. It is the rarest and most mature coal. It is a hard, compact variety of coal. It has the highest ranking amongst all the four types of coals. It has undergone the most metamorphosis. It has the highest fixed carbon content and the least impurities. It has the highest energy density amongst all types of coal. The formation of anthracite coal is shown in Fig 1. Fig 1 Formation of anthracite coal Anthracite coal normally occurs in old geological formations which have spent the longest time underground. It is the rarest and most mature coal which accounts for only around 1 % of the world’s total coal reserves. The major reserves of the anthracite coal are...

Lignite Coal

Lignite Coal Lignite coal is a natural resource which is readily available. It is often referred to as brown coal. It has some special characteristics which make it different from other coals. Lignite coal is a soft, brown, combustible, sedimentary rock formed from naturally compressed peat. It is considered to be the lowest rank of coal due to its relatively low heat content. It has lowest carbon (C) content amongst all types of coals. It is mined all around the world and is mainly used as a fuel for steam and electric power generation. Since it is not economical to transport lignite coal, it is not traded extensively on the world market when compared with higher grades of coal. Large reserves of lignite coal are available in limited areas of the world. Australia, USA and China have the major reserves of lignite coal. Germany has the largest number of power plants based on the lignite coal. In USA, most of the reserves are located in the North Dakota province while in India, the lignite coal reserves are in Neyveli in Tamil Nadu and in Rajasthan. Around 17 % of the world’s coal reserves are lignite coal. As the world’s oil and gas reserves decline, other sources have become attractive. That is why there is a sustained interest in the use of lignite coal. Coals are classified by rank according to their progressive alteration in the natural metamorphosis from lignite to sub bituminous coal to bituminous coal and to anthracite. Coal rank depends on the volatile matter, fixed carbon, inherent moisture, and oxygen, although no one parameter defines rank. Typically coal rank increases as the amount of fixed carbon increases and the amount of volatile matter decreases. Coal is a complex combination of organic matter and inorganic ash formed over eons from successive layers of fallen vegetation....

Reagents for Desulphurization of Hot Metal...

Reagents for Desulphurization of Hot Metal Sulphur (S), present in solid steel as iron sulphide (FeS) inclusions, has several detrimental effects on steel processing and on steel’s physical properties. During deformation, the iron sulphide inclusions act as crack initiation sites and zones of weakness. Such inclusions from sulphur adversely affect steel’s toughness, ductility, formability, weldability, and corrosion resistance. An increase in manganese (Mn) however, helps prevent formation of iron sulphide, which is highly detrimental to steel’s hot workability and also leads to severe cracking. Sulphur is such an undesirable element in steel that its removal is desired. The ever increasing requirements to steel properties and the growing demand for steel qualities and quantities with lowest sulphur contents of down to 0.001 %, has made it necessary for the steel makers to carry out the desulphurization of hot metal. Presently hot metal is regularly being desulphurized to below 100 ppm, and in some steel plants, to 10 ppm. Besides the increased requirements of steel quality, other reasons which necessitate desulphurization of hot metal are reduced scrap quality and increasing cost of high quality iron ores. In the desulphurization process, powdered desulphurization reagents are injected into the hot metal through an immersed lance using an inert carrier gas such as argon or nitrogen, as shown in Fig 1. Since desulphurization is a diffusion-controlled reaction, and related to the reactive surface area available for reaction, the desulphurization reagents are to be as fine grained as possible. However, flowability is reduced with very fine grains and hence it is necessary to find an optimum between efficiency and conveying ability. In order to obtain good flow characteristics, normally a fluxing agent is added during the grinding operation, so that pneumatic transport during injection does not pose any problems. Fig...

Crude Steel

Crude Steel  Crude steel is the term used for the first solid steel product which is produced during the solidification of liquid steel in a steel melting shop. Crude steel is part of saleable steel when it is supplied to customers for its use or for further processing. Crude steel is normally processed into finished steel either by rolling or by forging processes. World steel association also includes liquid steel which goes into production of steel castings under crude steel for statistical purpose. Various common types of crude steel products (Fig 1) include (i) ingot, (ii) slab, (iii) bloom, (iv) billet, (v) round, and (vi) dog bone section. Crude steel products are also semi-finished products since they need further processing for the production of finished steel. Fig 1 Common types of crude steel products Ingot Ingot is the product obtained by pouring liquid steel into cast iron mould of a shape appropriate for the subsequent processing generally by hot rolling or forging into semi-finished or finished products. The shape generally resembles a truncated pyramid or truncated cone. The side surfaces can be corrugated and the corners are more or less rounded. Depending on its subsequent conversion requirements, ingot can be dressed and/or hot scarfed or cropped. The usual cross section of ingot is square, rectangular, round, oval, or polygon. Ingots with square cross section are used for rolling into billets, rails and other structural sections, whereas, ingots with rectangular cross section, are generally used for rolling into flat products. These ingots usually have a width which is two times or higher than the thickness. Round ingots are used for the production of seamless pipes. Polygonal ingots are used to produce tyres, and wheels etc. Low capacity steel melting shops with induction furnaces produce very...

Macro-Segregation in Steel Ingots...

Macro-Segregation in Steel Ingots With the large scale reduction of the crude steel production through the ingot casting route, there is now-a-days a tendency of producing extremely heavy weight steel ingots weighing over 600 t and continuous cast strands with thickness over 450 mm and rounds with diameter over 800 mm. These large size crude steel products are mainly applied for retaining components like reaction vessels for nuclear power plant and rotating components such as drive shafts of gas turbines and generator rotors. These high value products require high quality of the as-cast crude steel products, and hence, the production of the heavy crude steel products with adequate control of the quality is a big concern for steelmakers worldwide. The macro-scale segregation of alloying elements during the casting of steel ingots continues to afflict the manufacturers of steel ingots, despite many decades of research into its prediction and elimination. Defects such as A-segregates are still common, and components are regularly scrapped due to their presence, leading to increased economic and environmental costs. With the growth of the nuclear power industry, and the increased demands placed on new pressure vessels, it is now more important than ever that today’s steel ingots are as chemically homogeneous as feasible. During the solidification of alloys (liquid steel), solute is partitioned between the solid and liquid to either enrich or deplete the inter-dendritic regions. This obviously leads to variations in the composition on the scale of micro-metres (micro-segregation). Macro-segregation is a composition inhomogeneity in the scale from several millimeters to centimeters or even meters. The effects of macro-segregation are critically important in the present day applications of steel ingots and hence the ability to predict segregation severity and location is very important and highly sought after these days. Almost...