Drying Technologies of Lignite Coals Jul20

Drying Technologies of Lignite Coals...

Drying Technologies of Lignite Coals Coals are generally ranked as anthracite, bituminous, sub-bituminous, and lignite, with anthracite being the oldest and lignite the youngest in the age. As coal ages, its moisture content decreases and heating value increases. The lignite coal is often being referred to as brown coal. It is considered to have the lowest rank, lowest carbon (C) content and highest moisture content. Moisture content in lignite coals can be even 60 % or more. Lignite coals are usually shallow buried facilitating its easy open mining. These coals besides high moisture content also have high volatile content and low calorific value (CV) with easy spontaneous ignition. High moisture content is the main restraint for the application of lignite coals. Moisture content of coal causes many difficulties during processing, storage, transport, grinding, and combustion. The high moisture content considerably reduces the CV and combustion efficiency of the coal. It also results into higher heat loss in the exhaust gas. In the combustion of lignite coals, the important part of the energy is consumed to evaporate the moisture inside the coal. The combustion of the high moisture content coal creates several problems such as the additional energy consumption for the moisture evaporation, the insufficient combustion and the additional exhaust discharge etc. Moisture content of the lignite coals can be classified into the following three types. Surface moisture – It is also known as external moisture. The moisture adheres to the surface of coal particulates or in the bigger capillary cavities. It is the moisture, which can be removed by the coal drying in air at ambient temperature (around 25 deg C). It depends on water conditions in deposit. Inherent moisture – It is a naturally combined part of the coal deposit. It is also...

Production of Ferro-Chrome Jul10

Production of Ferro-Chrome...

Production of Ferro-Chrome Ferro-chrome (Fe-Cr) is an alloy comprised of iron (Fe) and chromium (Cr) used primarily in the production of stainless steel. The ratio in which the two metals (Fe and Cr) are combined can vary, with the proportion of Cr ranging between 50 % and 70 %. Fe-Cr is frequently classified by the ratio of Cr to carbon (C) it contains. The vast majority of Fe-Cr produced is the ‘charge chrome’. It has a lower Cr to C ratio and is most commonly produced for use in stainless steel production. The second largest produced Fe-Cr ferro-alloy is the ‘high carbon Fe-Cr (HC Fe-Cr) which has a higher content of Cr and is being produced from higher grade chromite ore. Other grades of Fe-Cr are ‘medium carbon Fe-Cr’ (MC Fe-Cr) and ‘low carbon Fe-C (LC Fe-Cr). MC Fe-Cr is also known as intermediate carbon Fe-Cr and can contain upto 4 % of carbon. LC Fe-Cr typically has the Cr content of minimum 60 % with C content ranging from 0.03 % to 0.15 %.  However C content in LC Fe-Cr can be upto 1 %. Ferro-chrome (Fe-Cr) alloy is essential for the production of stainless steel and special steels which are widely used and are of high quality, typically characterized by a high corrosion resistance and a low tendency to magnetization. The processing cycle of Fe-Cr involves the chemical reduction of the chromite ore. Smelting of HC Fe-Cr ferro-alloy HC Fe-Cr and charge chrome are normally produced by the conventional smelting process utilizing carbo-thermic reduction of chromite ore (consisting oxides of Cr and Fe) using an electric submerged arc furnace (SAF) or a DC (direct current) open arc electric furnace. In SAF, the energy to the furnace is predominantly supplied in a resistive...

Production of Ferro-Silicon Jun27

Production of Ferro-Silicon...

Production of Ferro-Silicon Ferro-silicon (Fe-Si) is a ferro-alloy having iron (Fe) and silicon (Si) as its main elements. The ferro-alloy normally contains Si in the range of 15 % to 90 %. The usual Si contents in the Fe-Si available in the market are 15 %, 45 %, 65 %, 75 %, and 90 %. The remainder is Fe, with around 2 % of other elements like aluminum (Al) and calcium (Ca). Fe-Si is produced industrially by carbo-thermic reduction of silicon dioxide (SiO2) with carbon (C) in the presence of iron ore, scrap iron, mill scale, or other source of iron. The smelting of Fe-Si is a continuous process carried out in the electric submerged arc furnace (SAF) with the self-baking electrodes. Fe-Si (typical qualities 65%, 75% and 90% silicon) is mainly used during steelmaking and in foundries for the production of C steels, stainless steels as a deoxidizing agent and for the alloying of steel and cast iron. It is also used for the production of silicon steel also called electrical steel. During the production of cast iron, Fe-Si is also used for inoculation of the iron to accelerate graphitization. In arc welding Fe-Si can be found in some electrode coatings. The ideal reduction reaction during the production of Fe-Si silicon is SiO2+2C=Si+2CO. However the real reaction is quite complex due to the different temperature zones inside the SAF. The gas in the hottest zone has a high content of silicon mono oxide (SiO) which is required to be recovered in the outer charge layers if the recovery of Si is to be high. The recovery reactions occur in the outer charge layers where they heat the charge to a very high temperature. The outlet gas form the furnace contains SiO2 which can...

Production of Ferro- Manganese Jun19

Production of Ferro- Manganese...

Production of Ferro- Manganese Ferro-manganese (Fe-Mn) is an important additive used as a deoxidizer in the production of steel. It is a master alloy of iron (Fe) and manganese (Mn) with a minimum Mn content of 65 %, and maximum Mn content of 95 %. It is produced by heating a mixture of the oxides of Mn (MnO2) and iron (Fe2O3) with carbon (C) normally as coke or coal. Fe-Mn in a blast furnace (BF) with considerably higher Mn content than was possible earlier was first produced in 1872 by Lambert Von Pantz. The Fe-Mn produced had 37 % Mn instead of 12 % being obtained earlier. Metallurgical grade Mn ores having Mn content higher than 40 % are usually processed into suitable metallic ferro- alloy forms by pyro-metallurgical processes, which are very similar to the iron pyro-metallurgical processes. In its production process, a mixture of Mn ore, reductant (a form of C) and flux (CaO) are smelted at a temperature which is higher than 1200 deg C to enable reduction reactions and alloy formation. Standard grades of Fe-Mn can be produced either in a BF or in an electric submerged arc furnace (SAF). The electric SAF process, however, is far more flexible than the BF process, in that slags can be further processed to Si-Mn and refined Fe-Mn. The choice of process is also dependent on the relative price of electric power and coke. In a three-phase SAF, the electrodes are buried in the charge material. The raw materials are heated and the Mn oxides pre-reduced by hot carbon mono oxide (CO) gas form the reaction zones deeper in the furnace. The exothermic reactions contribute favourably to the heat required. Efficient production of HC Fe-Mn depends on the degree of pre-reduction which occurs...

Production of Silico-Manganese in a Submerged Arc Furnace Jun09

Production of Silico-Manganese in a Submerged Arc Furnace...

Production of Silico-Manganese in a Submerged Arc Furnace Silico-manganese (Si-Mn) is an alloy used for adding both silicon (Si) and manganese (Mn) to liquid steel during steelmaking at low carbon (C) content. A standard Si-Mn alloy contains 65 % to 70 % Mn, 15 % to 20 % Si and 1.5 % to 2 % C. Si-Mn alloy grades are medium carbon (MC) and low carbon (LC). The steelmaking industry is the only consumer of this alloy. Use of Si-Mn during steelmaking in place of a mix of high carbon ferro-manganese (Fe-Mn) alloy and ferro-silicon (Fe-Si) alloy is driven by economic considerations. Both Mn and Si are crucial constituents in steelmaking. They are used as deoxidizers, desulphurizers and alloying elements. Si is the primary deoxidizer. Mn is a milder deoxidizer than Si but enhances the effectiveness due to the formation of stable manganese silicates and aluminates. It also serves as desulphurizer. Manganese is used as an alloying element in almost all types of steel. Of particular interest is its modifying effect on the iron-carbon (Fe-C) system by increasing the hardenability of the steel. Si-Mn is produced by carbo-thermic reduction of oxidic raw materials in a three-phase, alternating current (AC), submerged arc furnace (SAF) which is also being used for the production of Fe-Mn. Operation of the process for the Si-Mn production is often more difficult than the Fe-Mn production process since higher process temperature is needed. The common sizes of the SAF used for the production of Si-Mn are normally in the range 9 MVA to 40 MVA producing 45 tons to 220 tons of Si-Mn per day. In the carbo-thermic reduction of oxidic raw materials, heat is just as essential for reduction as C is, due to the endothermic reduction reactions and a...

Steelmaking in Induction Furnace May24

Steelmaking in Induction Furnace...

Steelmaking in Induction Furnace Coreless induction furnaces have been used in the ferrous industry for over 50 years and are now one of the most popular means of melting and holding ferrous materials. Induction melting had dramatic growth during the 1960s based on line frequency technology, and later with the large-scale introduction of medium frequency power supply during the 1980s. Making of mild steel in the induction furnace was first experimented during early 1980s and it gained popularity when the production of sponge iron utilizing coal based process of rotary kilns became popular. Induction furnace is a type of electric melting furnace which uses electric current to melt metal. The principle of induction melting is that a high voltage electrical source from a primary coil induces a low voltage, high current in the metal (secondary coil). Induction heating is simply a method of transfer of the heat energy. Two laws which govern induction heating are (i) electromagnetic induction, and (ii) the joule effect. Coreless induction furnace comprises a relatively thin refractory crucible encircled by a water cooled copper coil excited from a single AC supply. When the coil is energized, the fluctuating axial magnetic field causes a current to flow in electrically conducting pieces of charge material within the crucible. The power induced in the charge depends on the physical properties of the material, the flux linking it and its geometric shape. Dependent on the resistivity of the material being melted, the coreless induction furnace converts electrical energy to heat the charge at an efficiency of between 50 % and 85 %, although furnace efficiency is further reduced by thermal losses from radiation from the melt surface and conduction through the furnace lining. Medium frequency induction furnaces which are commonly used for steelmaking use...