Limestone – Its Processing and Application in Iron and Steel Industry Jul07

Limestone – Its Processing and Application in Iron and Steel Industry...

Limestone – Its Processing and Application in Iron and Steel Industry Limestone is a naturally occurring and abundant sedimentary rock consisting of high levels of calcium carbonate (CaCO3) in the form of the mineral calcite. Some limestones may contain small percentage of magnesium carbonate (MgCO3). These limestones are known as dolomitic limestones. Limestone is also a very important industrial mineral. Its chemical properties make it a valuable mineral for a wide range of industrial/manufacturing uses. Limestone is also one of the vital raw materials used in production of iron and steel. Limestone, by definition, is a rock that contains at least 50 % of CaCO3 in the form of calcite by weight. There can be small particles of quartz (silica), feldspar (alumino-silicates), clay minerals, pyrite (iron sulphide), siderite (iron carbonate), and other minerals associated with the limestone. All limestones contain at least a few percent other materials. The Impurities in limestone can consists of silica (SiO2), alumina (Al2O3), iron oxide (Fe2O3), sulphur (as sulphides or sulphates), phosphorus (P2O5), potash (K2O), and soda (Na2O). Silica and alumina are the main impurities of limestone. The limestone which is used in ironmaking is required to contain at least 85 % of calcium carbonate and a low percentage of alumina. Similarly limestone which is used for steelmaking is required to contain at least 92 % of calcium carbonate and a very low percent of impurities especially the silica percentage. The main uses of limestone in iron and steel industry are (i) as a fluxing material, and (ii) other usage which consists of desulphurizing agent, coating of moulds of pig casting machine, neutralizing of acidic water, water treatment, waste water(effluent) treatment, flue gas treatment, and sludge and sewage treatment. It is also a component of synthetic slag. Limestone is...

Dolomite – A Useful Mineral...

Dolomite – A Useful Mineral Dolomite is also known as dolostone and dolomite rock.  It is a sedimentary rock which primarily consists of the mineral dolomite. It is found in sedimentary basins worldwide. Dolomite rock is similar to limestone rock. Both dolomite and limestone rocks share the same colour ranges of white-to-gray and white-to-light brown (although other colours such as red, green, and black are also possible). Both the rocks have approximately the same hardness, and they are both soluble in dilute hydrochloric (HCl) acid. The original mineral name ‘dolomie’ was given by NT Saussare, in 1792, in honor of the French geologist Deodat Guy de Dolomieu (1750–1801). Dolomite, the rock, contains a large proportion of dolomite the mineral. Ideal dolomite has a crystal lattice consisting of alternating layers of Ca and Mg, separated by layers of CO3 and is typically represented by a stoichiometric chemical composition of CaMg(CO3)2, where calcium and magnesium are present in equal proportions. Dolomite originates in the same sedimentary environments as limestone i.e. in warm, shallow, marine environments where calcium carbonate (CaCO3) mud accumulates in the form of shell debris, fecal material, coral fragments, and carbonate precipitates. Dolomite is thought to form when the calcite in carbonate mud or limestone is modified by magnesium-rich groundwater. The available magnesium facilitates the conversion of calcite into dolomite. This chemical change is known as dolomitization. Dolomitization can completely alter a limestone into a dolomite, or it can partially alter the rock to form a dolomitic limestone. Dolomite is a complex mineral. It is relatively a soft mineral which can be easily crushed to a soft powder. The mineral is an anhydrous carbonate mineral consisting of a double carbonate of calcium (Ca) and magnesium (Mg). It is chemically represented by CaMg(CO3)2 or CaCO3.MgCO3. It theoretically contains...

Standards and their importance for the Organizations...

Standards and their importance for the Organizations The modern and globalized world cannot exist without standards which are sup­porting cooperation, trade, health, safety, and economic growth etc. In fact, standards exist in almost all aspects of modern life. They range from standards in information and communication technology which ensure the interoperability of diverse components to standards for the quality of products or services, and underlie areas ranging from the harmonization of international accounting systems to the governance of the social and environmental performance of the organizations. Stand­ards have a huge influence on everyday life. They play a key role in an environment where an organization is to be at its best for achieving success. They are open access documents with no charge or license fee for their use, apart from the cost of its purchase. The development of standardization as an engineering activity was pioneered by Eli Whitney, who in 1793 invented the cotton gin, a machine for separating cotton fibres from their seeds. Whitney later introduced the production of interchangeable components for the manufacture of guns. Standardization of screw threads by Sir Joseph Whitworth dates back to 1841. Other instances of early standardization can be found in the dawning age of the railway industry, as the establishment of a standard width between the two rails on the railway track, the manufacture of railway couplings, air brakes and the signaling system called for increasing levels of standardized work. But major impetus to the development of standards came around the turn of the 20th century, when a large number of national standardization organizations were founded, including organizations that are nowadays known as the British Standards Institution (BSI) and the American National Standards Institute (ANSI). Their purpose was to create sets of rules for the design...

Dolomite – Its Processing and Application in Iron and Steel Industry Jun28

Dolomite – Its Processing and Application in Iron and Steel Industry...

Dolomite – Its Processing and Application in Iron and Steel Industry Dolomite is an anhydrous carbonate mineral. It is a double carbonate of calcium and magnesium (CaCO3.MgCO3). It is one of the important raw materials used in production of iron and steel. Dolomite contains theoretically 54.35 % of CaCO3 and 45.65 % of MgCO3 or 30.41 % of CaO, 21.86 % of MgO, and 47.73 % of CO2. However, in nature, dolomite is not available in this exact proportion. Hence generally the rock containing in the range of 40 % to 45 % of MgCO3 is usually called dolomite. The main uses of dolomite in iron and steel industry are (i) as a fluxing material (ii) for protection of refractory lining, and (iii) as a refractory raw material. Dolomite in iron and steel industry is normally used in three forms. These are (i) raw dolomite which is also the natural form of dolomite, (ii) calcined dolomite, and (iii) sintered dolomite. When dolomite is used as a fluxing material then it is used as either raw dolomite or calcined dolomite. When dolomite is used for the protection of refractories, it is used in calcined form and when dolomite is being used as a refractory raw material, it is used in the form of sintered dolomite. The uses and form of dolomite in iron and steel industry is shown in Fig 1. Fig 1 Uses and form of dolomite in iron and steel industry Processing of dolomite Dolomite after its mining has to undergo several processing before it can be used in various processes. The basic processes in the production of dolomite are (i) quarrying of raw dolomite, (ii) preparing mined dolomite for its use by crushing and sizing, (iii) calcining of raw dolomite, (iv) processing...

Waste Heat Recovery Devices...

Waste Heat Recovery Devices  Industrial furnaces are used for carrying out certain processes which requires heat. Heat in the furnace is provided by (i) fuel energy, (ii) chemical energy, (iii) electrical energy or (iv) a combination of these energies. Gases which are generated during the process leaves the furnace at a temperature which is the inside temperature of the furnace and hence have a high sensible heat content. Sometimes the exhaust gases carries some chemical energy, which raises the temperature of exhaust gases further due to post combustion because of this chemical energy. The heat energy contained in the exhaust gases is the waste energy since it gets dumped in the environment. However, it is possible to recover some part of this energy if investments are made in waste heat recovery devices (WHRDs). Methods for waste heat recovery include (i) transferring heat between exhaust gases and combustion air for its preheating, (ii) transferring heat to the load entering furnaces, (iii) generation of steam and electrical power, or (iv) using waste heat with a heat pump for heating or cooling facilities. WHRDs work on the principle of heat exchange. During heat exchange the heat energy of the exhaust gases gets transferred to some other fluid medium. This exchange of heat reduces the temperature of the exhaust gases and simultaneously increases the temperature of the fluid medium. The heated fluid medium is either recycled back to the process or utilized in the production of some utilities such as steam or power etc. The benefits of WHRDs devices are multiple namely (i) economic, (ii) resource (fuel) saving, and (iii) environmental. The benefits of these devices include (i) saving of fuel, (ii) generation of electricity and mechanical work, (iii) reducing cooling needs, (iv) reducing capital investment costs in...