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 Coal Coke Ferro Alloys Iron Ore Coal
Lignite - also known as brown coal - is coal with low organic maturity. It is characterised by its high moisture content and low carbon/energy content compared to coals such as anthracite. It is mainly used in power generation. Sub-bituminous coal is softer than bituminous coal and contains more moisture, making it less economic to transport long distances. Sub-bituminous has typical bed moisture levels of between 10 - 20% and a carbon content of between 71 - 77%. Bituminous coal is classified as coal which in terms of rank falls between sub-bituminous and semi-anthracite. Volatile matter can vary widely and bituminous coal is typically divided into three sub-groups - low volatile, medium volatile and high volatile. Bituminous coal has the required properties to generate steam electric power. Substantial quantities are used for power and heat applications in manufacturing as well as to make coke. Thermal/Steam coal describes coals considered particularly suitable for boiler use i.e. for power generation. Anthracite is the highest quality coal and is characterised by low volatile matter (always less than 10%) and high carbon content - it contains about 90% fixed carbon, more than any other form of coal. Anthracite has a semi-metallic lustre and is capable of burning without smoke (smokeless fuel). It is used in domestic and industrial applications. Anthracite is the least plentiful of all the coals. Large pellets of anthracite are used mainly for household heating and specialised industries such as glass, chemicals and as a reductant. Fine anthracite/semi-anthracite is used in the steel industry for pulverised coal injection (PCI), for sintering and briquetting and in the ferrometals market as a reductant. Steel works around the world are increasingly embracing Pulverised Coal Injection (PCI) as a way of lowering operating costs and extending the life of their coke ovens. PCI is a technique developed by the steel industry and involves the injection of coal directly into the blast furnace. PCI improves operational efficiency and replaces some of the coke used in the blast furnace. Coke is a higher cost fuel produced in coke ovens using more expensive coking coals. Traditionally, coals for PCI have been typically high volatile content coals. In recent times it has been recognised that some anthracite / low volatile coals which were previously considered of little value were suitable for PCI use and due to their very high carbon and energy content offer distinct financial advantages from : - a higher replacement ratio of coke than traditional coals; and
Based on the application, Electric Arc Furnace (EAF) Coke, in contrast with normal blast furnace coke and foundry coke, is unique, which requires lower CSR (Coke Strength after Reaction), higher CRI (Coke Reactivity Index) and proper Electric Resistivity as well. Electric Furnace are applied in the Steel, Ferro Alloys, Graphites,
Refractories and Fertiliser industries. Coke is also added to steel
ladles to re-carburize the melt after discharge from the furnace.
Ferroalloys like ferrosilicon, ferromanganese, ferrotitanium, etc,
are added in small and precise quantities for specific improvements
of steel properties.
Iron ore that contains a lower iron content must be processed to increase its iron content. This ore is crushed and ground into a powder so the waste material called gangue can be removed. The remaining iron-rich powder is rolled into balls and fired in a furnace to produce strong, marble-sized pellets that contain 60% to 65% iron. Sinter is produced from fine raw ore, small coke, sand-sized limestone
and numerous other steel plant waste materials that contain some iron.
These fine materials are proportioned to obtain a desired product chemistry
then mixed together. This raw material mix is then placed on a sintering
strand, which is similar to a steel conveyor belt, where it is ignited
by gas fired furnace and fused by the heat from the coke fines into
larger size pieces that are from 0.5 to 2.0 inches. The iron ore, pellets
and sinter then become the liquid iron produced in the blast furnace.
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Coal is classified
as either lignite, sub-bituminous, bituminous or anthracite, where lignite
contains the least carbon and anthracite the most.
As described
above bituminous coal is converted into 'metallurgical' coke and mainly
used in the steel blast furnace operation to melt the iron ore and remove
oxygen from the mix. The use of a high quality coke in a blast furnace
will result in a lower coke rate, higher productivity and lower hot
metal cost.
For ferroalloy
production, a submerged Electric Arc Furnace (EAF) is used, loaded with
selected and sized raw materials, such as quartz, wood, charcoal and
ores. During the process, these raw materials melt and chemically react.
The product that leaves the furnace is a molten metal, such as silicon,
ferrosilicon, ferronickel, thermal phosphorus, and zirconium. These
molten metals are cooled and further processed into the appropriate
size and grade for various applications.
Iron is the
fourth most abundant rock-forming element, producing hematite, magnetite,
siderite and geothite. Approximately 98% of the ore shipped in the world
is consumed in the production of iron and steel. Iron oxides can come
to the blast furnace plant in the form of raw ore, pellets or sinter.