Coke for railroads 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. This rule was quietly dropped, and cheaper coal became the normal fuel, as railways gained acceptance among the public. The smoke plume produced by a travelling locomotive seems now to be a mark of a steam railway, and so preserved for posterity. Wiki
Coke is a grey, hard, and porous fuel with a high carbon content and few impurities, made by heating coal or oil in the absence of air—a destructive distillation process. It is an important industrial product, used mainly in iron ore smelting, but also as a fuel in stoves and forges when air pollution is a concern.
The unqualified term “coke” usually refers to the product derived from low-ash and low-sulphur bituminous coal by a process called coking. A similar product called petroleum coke, or pet coke, is obtained from crude oil in oil refineries. Coke may also be formed naturally by geologic processes.
The industrial production of coke from coal is called coking. The coal is baked in an airless kiln, a “coke furnace” or “coking oven”. It has temperatures as high as 2,000 °C (3,600 °F) but usually around 1,000–1,100 °C (1,800–2,000 °F). This process vaporises or decomposes organic substances in the coal, driving off volatile products. Including water, in the form of coal-gas and coal-tar. The non-volatile residue of the decomposition is mostly carbon. In the form of a hard somewhat glassy solid that cement together the original coal particles and minerals.
Some facilities have “by-product” coking ovens in which the volatile decomposition products are collected. It is purified and separated for use in other industries, as fuel or chemical feed stocks. Otherwise the volatile byproducts are burned to heat the coking ovens. This is an older method, but is still being used for new construction.
Coke as a fuel
Coke is used as a fuel and as a reducing agent in smelting iron ore in a blast furnace. Additionally, the carbon monoxide produced by its combustion reduces iron oxide (hematite) in the production of the iron product. Coke is commonly used as fuel for blacksmiths.
Coke was used in Australia in the 1960’s and early 1970’s for house heating. It was an incentive for home use in the UK (so as to displace coal). After the 1956 Clean Air Act, which was passed in response to the Great Smog of London in 1952.
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. It may be combusted producing little or no smoke, while bituminous coal would produce much smoke. Namely, coke was widely used as a smokeless fuel. It is a substitute for coal in domestic heating following the creation of smokeless zones in the United Kingdom. Also in Highland Park distillery in Orkney roasts malted barley for use in their Scotch whiskey in kilns burning a mixture of coke and peat.
Coke may be used to make synthesis gas, a mixture of carbon monoxide and hydrogen.