Understanding Pulverized Coal Injection in Blast Furnace Oct21

Understanding Pulverized Coal Injection in Blast Furnace...

Understanding Pulverized Coal Injection in Blast Furnace Pulverized coal injection (PCI) is a well-established technology for hot metal (HM) production in a blast furnace (BF). It is practiced in most of the BFs and all the new BFs are normally built with PCI capability. The composition and properties of the coal used for injection can influence the operation, stability and productivity of the BF, the quality of the HM, and the composition of the BF gas. The coals being used for the PCI are described in the article under link ‘http://ispatguru.com/coal-for-pulverized-coal-injection-in-blast-furnace/’. The critical aspects of PCI systems include coal preparation, its storage and distribution to ensure uniform feed of coal to each tuyere without fluctuations in the coal delivery rate and its combustion through lance design and oxygen (O2) injection. Coal preparation Pulverization of coal is carried out in a single or multiple grinding mills (pulverizers) depending on the requirements. Grinding and distribution of the coal to the injection lances constitute a major operating cost. Coal reclaimed from coal storage is screened for the removal of the foreign material and any large lump of coal is crushed. The coal is then fed into the mill where it is pulverized and dried. Coal of the required size is transported out of the mill by the hot gas stream, collected in a bag filter and conveyed to the storage bins. Grinding and transport are carried out under an inert atmosphere to minimize the risk of ignition of the dry coal particles. The resultant particle size distribution of the pulverized coal affects it handleability in pneumatic transport equipment and, at high injection rates, its combustibility. Pulverizers grind coal to one of the two size fractions namely (i) pulverized coal where around 70 % to 80 % of...

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...

Coal for Pulverized Coal Injection in Blast Furnace...

Coal for Pulverized Coal Injection in Blast Furnace Injection of pulverized coal in the blast furnace (BF) was initially driven by high oil prices but now the use of pulverized coal injection (PCI) has  become a standard practice in the operation of a BF since it satisfy the requirement of reducing raw material costs, pollution and also satisfy the need to extend the life of ageing coke ovens. The injection of the pulverized coal into the BF results into (i) increase in the productivity of the BF, i.e. the amount of hot metal (HM) produced per day by the BF, (ii) reduce the consumption of the more expensive coking coals by replacing coke with cheaper soft coking or thermal coals, (iii) assist in maintaining furnace stability, (iv) improve the consistency of the quality of the HM and reduce its silicon (Si) content, and (v) reduce greenhouse gas emissions. In addition to these advantages, use of the PCI in the BF has proved to be a powerful tool in the hands of the furnace operator to adjust the thermal condition of the furnace much faster than what is possible by adjusting the burden charge from the top. Schematic diagram of a BF tuyere showing a pulverized coal injection lance is at Fig 1. Fig 1 Schematic diagram of a BF tuyere showing a pulverized coal injection lance Several types of coals are being used for PCI in the BF. In principle, all types of coals can be used for injection in BF, but coking coals are not used for injection since they are costly, have lower availability and are needed for the production of coke. Also, if coking coals are used for injections in BF, They lead to tuyere coking. Hence, coals used for injection...

Metallurgical Coal

Metallurgical Coal Metallurgical coal is also called ‘met coal’ or ‘coking coal. It is a bituminous coal which allows the production of a coke suitable to support a blast furnace (BF) charge. It is distinguished by the strong low-density coke produced when the coal is heated in a low oxygen (O2) environment or in absence of air to reduce mineral impurities (e.g. less sulphur, phosphorus). On heating, the coal softens, and volatile components evaporate and escape through pores in the mass. On cooling, the resultant coke has swollen, becoming a larger volume. The strength and density of coke is particularly important when it is used in a BF, as the coke supports part of the ore and flux burden inside the BF. Metallurgical coal possesses the ability to soften and re-solidify into a coherent, porous mass, when heated from 300 deg C to 550 deg C in the absence of air in a confined space. The conversion from coal to coke occurs in chambers called coke ovens where the volatiles from the coal escape, leaving behind what is referred to as metallurgical coke, which reaches a temperature of around 1,000 deg C to 1200 deg C before being removed from the ovens. The coking cycle is normally dependent on several parameters. Coke is used primarily as a fuel and a reducing agent in a BF. The gross calorific value (CV) of the metallurgical coal is greater than 5700 kcal/kg on an ash?free but moist basis. It presents unique plastic properties during carbonization which in turn produces a porous solid, high in carbon (C) coke. Metallurgical coals, when heated at a moderate rate in the absence of air, undergo complex and continuous changes in chemical composition and physical character. During carbonization, most bituminous coals, except those bordering...

Energy Management in Small and Medium sized Re-rolling mills...

Energy Management in Small and Medium sized Re-rolling mills Energy consumption in small and medium sized re-rolling mills takes place in two forms namely (i) electrical energy, and (ii) fuel or heat energy. Electrical energy is used directly in main rolling process for shaping of hot billets into rolled product (rolling mill, and shears etc.), in reheating furnace (coal pulverizer, blower, and pusher etc.) and also in auxiliary (roll turning machines, pumps, man coolers, overhead crane etc.), and shop lighting. Fuel energy is used in the reheating furnace for raising the temperature of the feed material to desired temperatures (generally 1150 deg C–1250 deg C). The division of the energy in these two forms normally varies from mill to mill based on the practices employed as well facilities installed in the re-rolling mills in SME (small and medium enterprise) sector. However, the share of electrical energy in small and medium sized mill generally varies in the range 20 % to 30 %. Consumption of fuel energy takes the major share of the energy consumption and usually constitutes 70 % to 80 %. From a theoretical perspective, the energy in hot rolling is primarily determined by the requirements of reheating of feed material. The theoretical energy for deformation is only 0.02 GJ/ton (around 5000 kcal/ton), compared to 0.83 GJ/ton (around 200,000 kcal /ton) for heating billets when charged cold in the reheating furnace. Though it is not technically feasible to achieve theoretical energy consumption figures, but the energy efficiency of the rolling mill is depends upon how close it is to the theoretical consumption. Management of electrical energy consumption Out of the total electrical energy consumed by a re-rolling mill, the share of the process of rolling is in the range of around 60 %...