Editing Coke (fuel) (section)

===Industrial coke furnaces===
[[File:Coke Ovens Abercwmboi.jpg|right|thumb|A coke oven at a [[smokeless fuel]] plant, [[Abercwmboi]], South [[Wales]], 1976]]

The industrial production of coke from coal is called coking. The coal is baked in an airless [[kiln]], a "coke furnace" or "coking oven", at temperatures as high as {{convert|2000|°C|°F|-2}} but usually around {{convert|1000|-|1100|°C|°F|-2}}.<ref>{{cite web |title= Coal and Steel |publisher= World Coal Association |url= http://www.worldcoal.org/coal/uses-of-coal/coal-steel/ |url-status= live |archive-url= https://web.archive.org/web/20120314103442/http://www.worldcoal.org/coal/uses-of-coal/coal-steel/ |archive-date= 14 March 2012 |date= 28 April 2015 }}</ref> This process vaporises or decomposes organic substances in the coal, driving off [[water]] and other volatile and liquid products such as [[coal gas]] and [[coal tar]]. Coke is the non-volatile residue of the decomposition, the cemented-together carbon and mineral residue of the original coal particles in the form of a hard and somewhat glassy solid.<ref>{{cite web |title=Glossary: Coke |url=https://www.eia.gov/tools/glossary/index.php?id=Coke |website=U.S. Energy Information Administration |access-date=16 January 2025}}</ref>

Additional byproducts of the coking are [[coal tar pitch]], [[ammonia]] (NH<sub>3</sub>), [[Hydrogen sulfide|hydrogen sulphide]] (H<sub>2</sub>S), [[pyridine]], [[hydrogen cyanide]] and carbon based material.<ref>{{Cite journal |last1=Tiwari |first1=H. P. |last2=Sharma |first2=R. |last3=Kumar |first3=Rajesh |last4=Mishra |first4=Prakhar |last5=Roy |first5=Abhijit |last6=Haldar |first6=S. K. |date=December 2014 |title=A review of coke making by-products |url=http://link.springer.com/10.3103/S1068364X14120072 |journal=Coke and Chemistry |language=en |volume=57 |issue=12 |pages=477–484 |doi=10.3103/S1068364X14120072 |s2cid=98805474 |issn=1068-364X}}</ref> Some facilities have "by-product" coking ovens in which the volatile decomposition products are collected, purified and separated for use in other industries, as fuel or chemical [[feedstock]]s. Otherwise the volatile byproducts are burned to heat the coking ovens. This is an older method, but is still being used for new construction.<ref>{{cite web|title=Cokemaking: The SunCoke Way|website = [[YouTube]]|url=https://www.youtube.com/watch?v=_rIQxXp2IQg|url-status=live|archive-url=https://web.archive.org/web/20160603074935/https://www.youtube.com/watch?v=_rIQxXp2IQg|archive-date=3 June 2016}}</ref>

==== Sources ====
[[Bituminous coal]] must meet a set of criteria for use as [[Metallurgical coal|coking coal]], determined by particular [[coal assay]] techniques. These include moisture content, ash content, [[sulphur]] content, volatile content, [[tar]], and [[plasticity (physics)|plasticity]]. The goal is to achieve a blend of coal that when processed will produce a coke of appropriate strength (generally measured by [[coke strength after reaction]]), while losing an appropriate amount of mass. Other blending considerations include ensuring the coke will not swell too much during production and destroy the coke oven through excessive wall pressures.<ref>{{Cite web |last=Brandcodax |date=2023-07-19 |title=Understanding Volatile Matter in Coal |url=https://www.nationalcoal.co.za/post/volatile-matter-in-coal |access-date=2024-12-12 |website=National Coal |language=en}}</ref>

The greater the volatile matter in coal, the more by-product can be produced. It is generally considered that levels of 26–29% 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. If the range of coal types is too great, the resulting coke is of widely varying strength and ash content, and is usually unsaleable, although in some cases it may be sold as an ordinary heating fuel. As coke has already lost its volatile matter, it cannot be coked again.<ref>{{Cite web |last=Brandcodax |date=2023-07-19 |title=Understanding Volatile Matter in Coal |url=https://www.nationalcoal.co.za/post/volatile-matter-in-coal |access-date=2024-12-12 |website=National Coal |language=en}}</ref>

Coking coal is different from thermal coal, but arises from the same basic coal-forming process. Coking coal has different [[macerals]] from thermal coal, i.e. different forms of the compressed and fossilized vegetative matter that compose the coal. The different macerals arise from different mixtures of the plant species, and variations of the conditions under which the coal has formed. Coking coal is graded according to its ash percentage-by-weight after burning:

* 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%)<ref>{{Cite web |url=http://www.coal.nic.in/content/coal-grades |title=Coal Grades |archive-url=https://web.archive.org/web/20160201122923/http://coal.nic.in/content/coal-grades |archive-date=1 February 2016 |work=Ministry of Coal}}</ref>