Commodity Knowledge
Commodity Knowledge
When used for many industrial processes, bituminous coal must first be "coked" to remove volatile components. Coking is achieved by heating the coal in the absence of oxygen, which drives off volatile hydrocarbons such as propane, benzene and other aromatic hydrocarbons, and some sulfur gases. This also drives off a considerable amount of the contained water of the bituminous coal.

Bituminous coal must meet a set of criteria for use as coking coal, determined by particular coal assay techniques. These include moisture content, ash content, sulfur content, volatile content, tar, and plasticity. This blending is targeted at producing a coke of appropriate strength (generally measured by coke strength after reaction (CSR), while losing an appropriate amount of mass. Other blending considerations include ensuring the coke doesn't swell too much during production and destroy the coke oven through excessive wall pressures.

The greater the volatile matter in coal, the more by-product can be produced. It is generally considered that levels of 26-29 percent of volatile matter in the coal blend are good for coking purposes. Thus different types of coal are proportionally blended to reach acceptable levels of volatility before the coking process begins.

Natural coke is formed when a coal seam is intersected by a volcanic intrusion. These intrusions heat the surrounding coal in an anoxic atmosphere producing coke in a zone (usually several meters) around the intrusion. However, the coke is of wildly varying strength and ash content and is generally considered unsaleable except in some cases as a thermal product-as it has lost its volatile matter it has lost the ability to be coked again.
  • Coke is the solid carbonaceous material derived from destructive distillation of low-ash, low-sulfur bituminous coal. Cokes from coal are grey, hard, and porous. While coke can be formed naturally, the commonly used form is human-made.
  • Coking coal is used in the manufacture of steel, where carbon must be as volatile-free and ash-free as possible.
  • Coking coal is heated to produce coke, a hard, grey, porous material which is used to blast in furnaces for the extraction of iron from the iron ore.
  • In England in the first years of steam railway locomotives, coke was the normal fuel. This resulted from an early piece of environmental legislation; any proposed locomotive had to "consume its own smoke". This was not technically possible to achieve until the firebox arch came into use, but burning coke, with its low smoke emissions, was considered to meet the requirement. However, this rule was quietly dropped and cheaper coal became the normal fuel, as railways gained acceptance among the general public.
  • Coke is used as a fuel and as a reducing agent in smelting iron ore in a blast furnace. It is there to reduce the iron oxide (hematite) in order to collect iron.
  • Since smoke-producing constituents are driven off during the coking of coal, coke forms a desirable fuel for stoves and furnaces in which conditions are not suitable for the complete burning of bituminous coal itself. Coke may be burned with little or no smoke under combustion conditions, while bituminous coal would produce much smoke.
  • Discovered by accident to have superior heat shielding properties when combined with other materials, coke was one of the materials used in the heat shielding on NASA's Apollo program space vehicles. In its final form, this material was called AVCOAT 5026-39. This material has been used most recently as the heat shielding on the Mars Pathfinder vehicle. Although not used for modern day space shuttles, NASA had been planning to utilize coke and other materials for the heat shield for its next generation space craft, named Orion, before that project's cancellation.[citation needed]
  • Coke was widely used as a substitute for coal in domestic heating following the creation of Smokeless zones in the United Kingdom when the government paid for new grates suitable for the fuel. Ironically the grates required the use of a gas fired poker to light the fuel so the new installation included installation of a gas line adjacent to the fireplace. Most consumers converted to a gas fire designed to work with an existing chimney within a few years.
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