Kömür çeşitlerine göre, termal kömür (thermal coal) olarak genellikle turba, linyit ve alt bitümlü kömür türleri kullanılır
Thermal coal, also known as steam coal, is used for power and heat generation. In electricity generation, thermal coal is ground to a powder and fired into a boiler to produce heat, which in turn converts water into steam. the steam is used to move turbines to generate electricity. They usually have high ash content ranging from as low as 20% to as high as high as 50%. In Indian coal industry the Non-Coking coal grades have been categorised into 17 bands according to their Gross Calorific Value. The G17 band has the lowest with 2200–2500 KCal/Kg .
As per ranks of the coal the Peat, Lignite and Sub-Bituminous ranges of coal are usually used as Thermal Coal.
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Metallurgical coal/Coking Coal on the other hand is used in metallurgical process such as in smelting of Iron to make steel. They are usually used both as fuel and reducing agent in the form of coke. Coke is a porous, hard black rock of concentrated carbon that is created by heating bituminous coal without air to extremely high temperatures. The coal is baked in a coke oven which forces out impurities to produce coke, which is almost pure carbon. These kinds of coal are usually low in ash, Sulfur and Phosphorous Content. Although ash content can be regulated by washing process, low contents of sulfur and phosphorous are necessary as they tend to migrate to metals.
Mettalurgical Coke
The grades of coking coal are
- Steel Grade I (Ash content not exceeding 15%)
- Steel Grade II (Exceeding 15% but not exceeding 18%)
- Washery Grade I (Exceeding 18% but not exceeding 21%)
- Washery Grade II (Exceeding 21% but not exceeding 24%)
- Washery Grade III (Exceeding 24% but not exceeding 28%)
- Washery Grade IV (Exceeding 28% but not exceeding 35%)
Usually Bituminous range coals are used as coking coal.
The GCV of coking coal is usually around 6000 KCal/Kg.
Footnotes
Caking coal is the Coal which will form a solid residue on heating to very high temperature around 1100 deg Celsius in the absence of oxygen (or very less amount of oxygen).
Non-Caking coal is the Coal which will form powder residue on heating to very high temperature around 1100 deg Celsius in the absence or very less amount of oxygen.
Caking coal is called as Coking coal if the solid residue formed is coke (hard but porous solid form of carbon)
Why Coke is prepared?
For Steel Industry, the Iron Ore must be reduced with almost PURE Carbon. Coke is nothing but a hard, porous mass of carbon formed by heating the Coking coal in the absence of oxygen to very high temperature.
Coal other than Coking coal are used as thermal coal in the power plants.
Usually Coking coal consists of less sulphur (less than 0.75% calculated based on DMMF (Dry, mineral matter free) basis, less phosphorus (0.15 to 0.25% on DMMF basis) and less mineral matter (which will turn into ash on burning)
Thanks for A2A Rashmita Sethy
Caking Coal - Coal that softens and agglomerates on heating and after volatile matter has been driven off at high temperatures; produces a hard gray cellular mass of coke. All caking coals are not good coking coals.
Coking Coal - These coals, when heated in the absence of air, form coherent beads, free from volatiles, with strong and porous mass, called coke.
These have coking properties
Mainly used in steel making and metallurgical industries
Also used for hard coke manufacturing
The Table attached herewith sets forth the various Gross Calorific Values (GCV) based bands of coking and non-coking coal:
Thermal coal or steaming coal is burned for steam to run turbines to generate electricity either to public electricity grids or directly by industry consuming electrical power (such as chemical industries, paper manufacturers, cement industry and brickworks). During power generation the coal is ground to a powder and fired into a boiler to produce steam to drive turbines to produce electricity.
- Major producers: China, Australia, South Africa, Colombia, Russia, United States, Indonesia
- Major exporters: Australia, South Africa, Colombia, Russia, United States, Indonesia
- Markets: Thermal coal demand rose dramatically during 2007 and 2008, primarily due to the increasing demand for power generation in the Far East. Prices also hit historic highs in mid-2008 of around US$200. Although the global financial crisis has had an impact on power generation forecasts, electricity production from coal is continuing at much the same pace as before and energy experts believe that thermal coal prices are unlikely to fall below these levels in the longer-term.
- Demand: Forecast to increase at a steady pace through to 2013 and beyond.
Metallurgical coal or coking coal is used in the process of creating coke necessary for iron and steel-making. Coke is a porous, hard black rock of concentrated carbon that is created by heating bituminous coal without air to extremely high temperatures.
- Major producers: Australia, Canada, United States
- Major exporters: Australia, Canada, United States
- Markets: Coking coal demand and prices reached record price levels during 2008 mainly because of China’s dramatic increase in production of steel in recent years and demand for coking coal. Indian steel mills were also driving the demand for coking coal, but not on the scale of the Chinese. The credit crisis and global economic slowdown have undercut customers in key markets – construction, automobiles and industrial equipment – sending prices tumbling and prompting steel companies to slash production, scale back shipment forecasts, delay expansion and cut back the workforce.
- Demand: Dramatically decreasing with decreased demand for steel
Overall, some analysts say the fall of of coking coal prices has not had an impact on thermal coal prices. The medium to long-term stability of thermal coal demand and prices is expected to continue. Coking coal demand, on the other hand, is expected to remain low.
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