Steel production relies heavily on coal used for metallurgical. This is made by heating bituminous coke (which must be low in sulfur and ash) without oxygen. Pyrolysis removes most volatile compounds, leaving a carbon-rich form. This coke is not a fuel, but it can be burned in a blast furnace to produce steel.
The high temperatures initially cause the coals to contract and soften. As the coal heats up, it starts to swell. As the coal heats up, it begins to swell. These gases and smaller molecules are referred to as coal tar. Other chemicals in coal tar can also be helpful, like sodium chloride, which reduces the melting temperature of iron, and lowers its brittleness.
The coal that has swelled up and been broken down is now a plastic-like mass with highly organized liquid-crystalline regions. The chemical reactions that follow ultimately repolymerizes the coal tar, resulting in a polymeric substance known as metallurgical Coke. This is a complex mixture whose properties are affected by the characteristics of the coal used as input.
This metallurgical carbon coke is also very low in ash and sulfur, and can withstand high temperatures. In fact, it is used in the recarburization and enrichment process of pig iron to improve its quality, and it can also be found in some types of steel alloys.
The properties and temperature of the metallurgical slag are affected by its calcination. The more time it takes for calcination to take place, the harder and less volatile the material will be. Coke is difficult to produce with conventional equipment because the temperatures are too high. The new method allows for lower-ranking coals to also be used.
Fluid coking is a newer method of producing coke that uses raw coal continuously in a heated reactor, rather than using the older batch-delayed-coke process. Fluid coking is used around the world.
This is an extremely complex process that requires a great deal of detail-oriented attention and expert knowledge. The result is a very consistent, high-quality metallurgical coke. It is important to maintain this consistency in order to produce steel that can be cast and welded successfully. It is also determined by the quality of metallurgical coal whether it can be used for blast furnaces that require a consistent product. The best coke for metallurgical use has low ash, sulfur content, high fixed-carbon content, and minimal porosity. These qualities are important because they directly affect the quality of the resulting steel. Currently, the quality of metallurgical coke varies widely because it is being made from different grades of coal and blends of up to 20 different types.
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