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...

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...

Blast Furnace gas generation and usage Mar18

Blast Furnace gas generation and usage...

Blast Furnace gas generation and usage Blast furnace (BF) gas is a gaseous by product which is generated while producing hot metal (liquid iron) in a blast furnace. The operation of the blast furnace is controlled to produce hot metal of a specified quality and during this production BF gas comes out from the furnace top. During production of hot metal in a blast furnace, hot air blast is blown in the furnace through the tuyeres. The oxygen of the blast reacts with the coke. The gas produced by this reaction moves up the furnace shaft which has been charged with ores, fluxes and coke. After a number of chemical reactions and a travel of around 25-30m the BF gas comes out of the furnace as a heated, dust laden and lean combustible gas. Around 1500-1700 Cu m/ton of hot metal of BF gas is generated during the process. Though the purpose of partial combustion of carbon in a blast furnace is to remove the oxygen from the ore but the volume of gas generated in a blast furnace makes the blast furnace as a gas producer. The percentage of CO and CO2 in BF gas is directly related to the amount of carbon in the charged coke and amount of CO2 in the charged flux (Limestone and dolomite). The coke rate (The rate of carbon consumption) in the blast furnace depends mainly upon the type of the hot metal to be made, the chemical and the physical characteristics of the charged materials, the distribution of the materials in the furnace stack, the temperature and the oxygen enrichment of the hot air blast. The total amount of CO+CO2 gases by volume in the BF gas at the furnace top is around 40% of the...