Old King Coal Part 1: Coal Fuel
In this new series, Martin Pitt outlines coal’s historic place, first as the basis for solid fuels, then gaseous fuels, chemicals, colours and pharmaceuticals
COAL made the Industrial Age and global warming is evidence of its huge success as a fuel. It is a remarkable substance which was once an essential subject in British chemical engineering degrees, but has been largely dropped, along with coal usage in the UK. However, global production in 2024 was 8.7bn t, the highest ever, and almost twice what it was in 2000.
Coal formation
Coal starts off as peat – the accumulated debris from ancient forests and wetlands which gets pushed down into the earth by sediment and geological movement. Microbial action is followed by heat and pressure, depending on how deep the layer is pushed into the earth. If at high temperatures (170–250°C) for long enough, virtually all the organic material decomposes and is lost as small molecules of H2O, CO2, CH4 etc, leaving only carbon plus inorganic compounds from the soil and plant. Coalmines often have these gases in them. CH4-rich ones are a fire hazard, known as firedamp (from the German meaning fire vapour). CO2-rich ones are suffocating and known as whitedamp or chokedamp. CO can also be generated from combustion as the coal is exposed to air, a poison called blackdamp.
The least converted is lignite (brown coal, though it may be black) with 25 to 35% carbon, and a lot of water. Today it is only used in steam boilers for electricity generation. Sub-bituminous has 35–45% and is used for the same purpose, but with a higher heating value. Most commercial coal is in the 45–78% carbon range and is known as bituminous because it contains a complex organic tar called bitumen, asphalt or pitch. The most completely converted coal is known as anthracite (hard coal), from 78 to 90% carbon which is the hardest to ignite but burns hottest with virtually no smoke. Further conversion leads to graphite, which is 99.9% carbon. The geologic age from 360 to 300 million years ago is called the Carboniferous era because of the substantial amounts of coal that were laid down. These ancient trees did not rot as they do today because it took until 280 million years ago for fungi to develop the capability to digest lignin, the key ingredient for woody plants. All anthracite dates from this era. Bituminous coal is at least 200 million years old.
Types of coal: Jet
A rare type of coal is formed from whole pieces of wood in low oxygen salt water with a suitable pressure history from the Jurassic Age about 180 million years ago. Unlike other coals it is warm to the touch, less brittle and can be polished to a high gloss, so is used for jewellery or other decorative items. It also has electrostatic properties like amber. The name is from ancient Greek, Gagae, the place where it was found. It is the origin of the term jet black.
It is typically found in isolated lumps – such as branches, logs, and occasionally larger deposits – within other minerals like coal, shale and ironstone. It was only rarely discovered as a thin seam, which is why it wasn’t mined underground until Victorian times. Carved items including a beetle and a Venus dating from 10,000 BC have been found in Germany, and carvings from 4,000 BC in China. In Britain, high quality jet can be found on the beaches around Whitby, North Yorkshire, and from around 4,000 BC and throughout the Bronze Age, there was an active trade in beads – later expanding to include buttons and more complex items – across the country, as well as to Ireland and France.
Jet was a popular choice for jewellery in Victorian times, particularly for mourning attire, in a society where large families and frequent deaths were common.
Ancient times
Coal was dug out of a surface outcropping and used in fireplaces 25,000 years ago near what is now Ostrava, in the Czech Republic. This was an Ice Age society, with mammoth and reindeer around the settlement, and few trees, so the coal must have been a treasure. After the end of glaciation in about 10,000 BC there was plenty of wood and no evidence of coal usage until around 1600 BC in Bronze Age China. A large and sophisticated settlement selectively mined and stored the better bituminous coals from several outcroppings 3 to 4 km away for domestic and metallurgical purposes. The earliest known charcoal kilns (~2400 BC) are nearby, but from 2200 BC there was a global cooling which affected many civilisations, greatly reducing tree cover in this area. Moving from charcoal to coal is an example of human adaptation to climate change.
Greek polymath Theophrastus (371–287 BC) wrote a treatise On Stones where he describes a rock in Italy which could be made to burn and was used by smiths. The first written account of regular coal use in China dates from sometime after 200 BC. It was noted that food tasted different when cooked with coal rather than bamboo. In Roman Britain from 200–400 there is evidence of coal being used in metalworking, central heating and cremation, from nearby surface outcrops.
Middle Ages onward
I have myself picked lumps of coal from the beach in Northumberland, washed in by storms from seams exposed underwater. It was here and on the Firth of Forth in Scotland that the British coal industry began in the 13th century, digging out seams near the surface. This seacoal was an alternative to charcoal made from wood (coal meaning any solid fuel, as it is used in the Bible eg “coals of fire”). It is a bituminous coal, easier to ignite than anthracite and much hotter than wood or peat, hence welcomed by blacksmiths. It was also used for burning limestone CaCO3 to get quicklime CaO and thus slaked lime Ca(OH)2 used for mortar and chemical purposes. A coastal trade soon developed, down to London, with the names Saccoles [Seacoals] Lane and Lime-Burners Lane indicating the trades. It was later adopted by brewers and dyers, so beginning seven centuries of coal usage.
Elsewhere the Venetian traveller Marco Polo (1254–1324) described extensive use of coal in China, and the Aztecs in South America used coal for heating and cooking from 1350.
In 1575, an exceptional early mine was created by Scottish entrepreneur Sir George Bruce of Carnock (1550–1625). A tunnel under the sea emerged via a 12 m vertical shaft into an artificial island, from where it was loaded into ships.
In Britain, coal powered the Industrial Revolution (1750–) by supplying more energy than wood, as well as the higher temperatures and carbon needed for iron and steel production. Initially it was by digging pits or horizontally from surface outcrops on hillsides, with deep mining beginning in 1780. It was usual for whole families to work, often largely naked because of the heat. Men and older boys, called getters, would work at the seam with pickaxes and shovels to put it onto barrows. These were then pulled or pushed by women and older children, known as hurriers or thrusters. Smaller children worked in pairs. Meanwhile, the smallest children worked as trappers, opening and closing wooden doors to let barrows through, to minimise disturbance to the mine ventilation. This was all done crawling and mostly in darkness. There were few candles because they were expensive for miners to buy. Shifts were of 12 hours, six days a week, all the time breathing dust, and with frequent injuries. Children generally started at age eight, though some were as young as five. It wasn’t until 1842 that a UK Act of Parliament prohibited children under the age of ten from working in mines. Horses had been used underground to pull carts from 1750, but the act greatly increased their use, especially smaller ponies. The last pit pony emerged from a British mine in 1994.
The steam engine was developed initially to pump water from mines. In 1814 English engineer George Stephenson (1781–1848) built the first coal-powered locomotive which was used to haul coal up a hill from Killingworth colliery. Railways spread across the world in tandem with coal mining, which provided both fuel and materials for building engines and rails, while railways in turn enabled the transport of coal and other minerals. Steam-powered diggers and trucks facilitated large-scale open-cast coal mining.
Explosives have been used in mining since 1627, and were naturally adapted to coal mining, accounting for nearly half the industrial use in the US by 1946. As well as the risk from rock falls and explosions of coal dust, the fumes afterwards and absorption of chemicals through the skin were harmful and often lethal.
Pneumatic drills began to appear in the 1850s. In 1871 Scottish ironmaster John Alexander (1825–1895) created the first pneumatic coal-cutting machine (a chainsaw), and in the 1900s the adoption of electric motors made them generally viable. Irish inventor Richard Sutcliffe (1849–1930) invented his own coal-cutter in 1892, but also in 1905 the coal conveyor belt to reduce the need for carts. However, millions of miners still worked in dangerous and unhealthy conditions, made noisier by machinery. About 2.7m still do today, most in China and India.
Types of coal: Coke
Coke is the equivalent of charcoal: bituminous coal heated in the absence of air so that volatile materials are lost and what remains is a porous material, largely carbon. This is a hotter, cleaner fuel. As a child I remember moving from a house with a coal fire to one with a coke one, fitted with a gas poker to light it. How pleased we were not to need kindling, and not to have the dirt and smell of coal! Its first use in Britain was in 1642, to roast malt for beer without coal fumes. This would have been made like charcoal, in a pile covered with earth or turf and a fire in a central shaft which needed to be tended day and night for over a week. The charcoal burner got the fumes, but far away from the brewery. In 1709 British ironmaster Abraham Darby (1677–1717) was the first to operate a blast furnace with coke instead of charcoal, a major step in iron production for the Industrial Revolution. In the next century coke was increasingly made in brick ovens, which took only three days. However, China had been making coke in ovens since the fourth century for its metal industries. Coals were selected for their low ash content and their ability to produce coke of sufficient strength for the intended use. The strongest are required for use in steelmaking because the coke supports the weight of iron ore above it in a blast furnace, and require low sulfur and phosphorus. Suitable coals may be called coking or metallurgical coal. Others are referred to as thermal coal or steam coal. The key understanding of coal’s microstructure, how the different grades would burn, and what sort of coke it would make, was achieved by British X-ray crystallographer Rosalind Franklin (1920–1958) from 1942–45 working for the British Coal Utilisation Research Association. She later found the structure of DNA but did not share in the Nobel Prize which resulted.
Coal smoke
In 947 Persian traveller Al-Mas’udı (896–956) wrote of the smoke and fumes from coal in China.
In Britain, the industrial use of coal was already causing offence to important people in the 13th century. Queen Eleanor (wife of Henry III) had to leave Nottingham in 1257 because of the foul air. In 1273 London banned the use of soft coal (lignite) within city walls because it was “prejudicial to health”. In 1306 and 1307 Royal proclamations were issued, banning the use of seacoal in the City of London, with little effect. From the 14th century, new designs of domestic fires to burn coal instead of wood, were produced, adding to the pollution, initially around coalfields, but by the 16th century in most cities, as deforestation had greatly increased the cost of wood.
In 1661 the English writer John Evelyn (1620–1706) published a pamphlet Fumifugium or the Inconvenience of Aer and Smoke of London Dissipated: Together with Some Remedies Humbly Proposed. He observed that “almost half of the people who die in London do so from disorders of the throat or lungs. The inhabitants are never free from coughs or persistent rheumatism” (rheumatism meaning phlegm). This was sent to the King and parliament, but no action was taken. Their experts advised that, on the contrary, smoke was beneficial by inhibiting infections.
The new trade of chimney sweeping came into being, with small children as young as four struggling up chimney flues with a brush in hand. In 1775 English surgeon Percivall Pott (1714–1788) identified the first industrial disease – cancer of the scrotum in these boys, from soot chemicals. The Chimney Sweepers Act of 1788 raised the minimum age to eight and introduced some minimal protections.
English chemist Luke Howard (1772–1864), sometimes called the father of meteorology, identified the heat island effect which causes smog to linger in his book The Climate of London in 1820.
In 1852, Scottish analytical chemist Robert Angus Smith (1817–1884) identified sulfur in coal combusting to SO2 as the major harmful chemical in flue gas and coined the term “acid rain”. His expertise in flue emissions led him to become Her Majesty’s Inspector of Alkali Works with four inspectors under him following the Alkali Act 1863 to control emissions of HCl from Leblanc soda ash works. Meanwhile in the US, Pittsburgh in 1868 was described as “hell with the lid taken off”. In 1905 London’s combination of smoke and fog was first called smog by the chairman of the Coal Smoke Abatement Society.
Despite public protests and government enquiries it was not until the 1956 Clean Air Act that the UK took proper action against coal smoke. It has been followed by similar legislation to limit industry and mandate the use of smokeless fuels in many countries. I remember a major smog in Birmingham from about this time.
Increasing technology has been used to remove particles, acid fumes and mercury vapour from coal flue gas, and the change to coke or anthracite for domestic use has resulted in cleaner air in many cities. However, there are thousands of burning coalfields around the world which pollute the air for locals, often those working in mines. Some have been burning for centuries; others are underground or opencast mines which have caught fire. China loses an estimated 20m t of coal a year in this way, and India’s prime coalfield in Jharia is notorious for the smoke and fumes suffered by its residents.
Clean coal
This term originally meant coal which had all extraneous objects and any obvious mineral lumps removed by hand, and was then washed, which increased the fuel content, and reduced ash, soot and grit from the flue. By shaking while washing, heavier particles tended to go to the bottom, and lighter ones were washed away – this is the technique people use when panning for gold on a sieve. A 1556 book by Georgius Agricola (1495–1555) De re metallica vol VIII shows manual but industrial versions of what is now known as a jig washer and instructed in their use for mineral cleaning.
For minerals it is the lighter non-metal-bearing particles which should be rejected, but for coal it is the heavier ones. The first modern coal washing plant was constructed by German mining engineer Ernst Friedrich Wilhelm Lindi (1779–1852) in 1810 at Freital, Germany.
This also tended to reduce sulfur emissions, since most of the sulfur content typically comes from mineral particles (metal sulfides). However, when concerns about acid fumes were taken seriously enough, coal washing was supplemented by washing with alkali. This removal of sulfur before burning became the new meaning of “clean coal” in 1972 (via Scientific American). In 2018 US president Donald Trump (1946–) talked of “trains loaded up with clean coal – beautiful clean coal” and has regularly used the phrase in his second term.
Since 2009 the term has been used for technologies to control emissions of CO2, by carbon capture, which is really a misnomer since it relates to the product, not the coal. Trump seems to misunderstand this.
Martin Pitt CEng FIChemE is a regular contributor. Read other articles in his history series: https://www.thechemicalengineer.com/tags/chemicalengineering-history
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