# The fossil-fuel revolution: Coke, iron and the steam engine

Source page: https://www.materialinsights.org/learn/energy/fossil-fuel-revolution/p2/

[Understanding Energy](https://www.materialinsights.org/learn/energy/) / [Module 5: The fossil-fuel revolution](https://www.materialinsights.org/learn/energy/fossil-fuel-revolution/) Part 2 of 5

## Coke, iron and the steam engine

Coal provided heat first. To become the engine of industry it needed two more inventions: a way to make iron without charcoal, and a machine that turned heat into motion. Coke solved the first; the steam engine, improved step by step over a century, solved the second. Together they gave the world railways, steamships and mechanised factories.

### 2.1 Coke freed iron from the forest

Iron was the material of tools, nails, hoops, pots and weapons, and its production devoured wood. Iron ore had to be heated with a fuel that also acted as a chemical agent, pulling the oxygen out of the ore. For centuries that fuel was charcoal, made by slowly smouldering wood in covered heaps. Charcoal making used several units of wood for each unit of charcoal, and an iron furnace could strip the surrounding woodland in a few years.

Raw coal does not work well in a blast furnace. It contains sulfur and other impurities that spoil the iron, and it softens and clogs the furnace when heated. The answer was coke: coal baked in the absence of air until the volatile parts are driven off, leaving a hard, porous, nearly pure carbon that can bear the weight of the ore above it and let the hot air blast pass through.

Abraham Darby first smelted iron with coke at Coalbrookdale in Shropshire in 1709. Adoption was slow. Coke iron was at first suited mainly to castings, and charcoal iron kept its place for decades. Only in the second half of the 18th century, helped by better blowing engines, did coke displace charcoal across Britain.

Once it did, iron output was no longer limited by forests, and the link between coal and metals that still defines heavy industry was formed. Even now most of the world's steel starts in a blast furnace fed with coke made from a special grade of coal, which is why coking coal is traded as a separate commodity from the thermal coal burned in power stations.

Process flowchart From coal to iron Inputs **Coking coal**about 1.3 to 1.5 t per tonne of coke **Iron ore**about 1.5 t per tonne of iron Process steps 1 **Coke oven**

coal heated without air; volatiles driven off, leaving porous carbon
 2 **Blast furnace**

coke burns to supply heat and carbon monoxide, which strips oxygen from the ore
 Outputs **Pig iron**1 t, carrying about 4% carbon **Furnace gas and slag**by-products

Quantities are typical modern orders of magnitude; early furnaces used far more fuel per tonne.
 Source: Smil, Still the Iron Age: Iron and Steel in the Modern World (2016), via Smil Mastery Course, M5 'Coke, iron and the steam engine'  Worked example

#### The wood bill of charcoal iron

In the pre-coke era, producing a tonne of pig iron could take several tonnes of charcoal, and each tonne of charcoal could take five or more tonnes of wood. A single furnace making a few hundred tonnes a year therefore consumed the sustainable output of thousands of hectares of woodland. Coke replaced that land with a few tonnes of coal per tonne of iron, dug from a seam.

- Smil, Energy and Civilization: A History (2017) · via Smil Mastery Course, M5 'Coke, iron and the steam engine'
- Smil, Still the Iron Age: Iron and Steel in the Modern World (2016) · via Smil Mastery Course, M5 'Coke, iron and the steam engine'

### 2.2 Newcomen to Watt: the slow climb of steam efficiency

Coal mines had a water problem. The deeper the shafts, the more water flooded in, and horses turning pumps could not keep up. Thomas Newcomen's engine of 1712 solved it with a simple, clumsy idea. Steam filled a large cylinder under a piston, a spray of cold water condensed it, and the vacuum left behind let the weight of the atmosphere push the piston down. A beam attached to the piston worked the pump.

The engine was enormous and slow, and it wasted almost all of its fuel. Its efficiency was around 0.5%: of every 200 units of chemical energy in the coal, about one emerged as useful work. That was acceptable only at a coal mine, where the fuel was the unsaleable small coal lying around the pithead. Its power was a few kilowatts, around 4 kW for typical engines.

James Watt spotted the main waste. Because the same cylinder was heated by steam and then cooled by water every stroke, much of the fuel went into reheating metal. His separate condenser, patented in 1769, kept the cylinder hot and condensed the steam elsewhere. That raised efficiency several times over. From the 1780s, Watt and his partner Matthew Boulton built engines that produced rotary motion, around 20 kW, able to turn the machinery of textile mills and workshops.

Watt was also a cautious defender of his position. Smil notes that he guarded his patents aggressively and opposed the use of high-pressure steam, which he thought dangerous. Major progress with high-pressure engines came only after his patent expired in 1800.

Process flowchart From coal to pumping work in a Newcomen engine Inputs **Coal**1 kg, about 25 MJ Process steps 1 **Boiler**

coal heat raises low-pressure steam, with large losses up the chimney
 2 **Cylinder and condensing spray**

steam condensed in the same cylinder; most heat lost reheating metal
 3 **Beam and pump**

atmospheric pressure drives the piston; friction losses
 Outputs **Useful pumping work**about 0.13 MJ (about 0.5%)

Watt's separate condenser lifted the useful output to several times this.
 Source: Smil, Energy and Civilization: A History (2017), via Smil Mastery Course, M5 'Coke, iron and the steam engine'  In the data

#### What 0.5% means

A Newcomen engine burning 1 tonne of coal, about 25 GJ, delivered roughly 125 MJ of useful work. That is roughly what a fit labourer working a pump delivers in 40 to 60 days. Burning a whole tonne of coal to replace two months of one man's effort made sense only where coal was almost free. Watt's improvements cut the coal needed for the same work by a factor of three to five.

- Smil, Energy and Civilization: A History (2017) · via Smil Mastery Course, M5 'Coke, iron and the steam engine'
- Smil, Energies: An Illustrated Guide to the Biosphere and Civilization (1999) · via Smil Mastery Course, M5 'Coke, iron and the steam engine'

### 2.3 High-pressure steam made engines mobile and reshaped transport

Low-pressure engines were too heavy and bulky to move themselves. High-pressure steam, pioneered in the early 1800s by Richard Trevithick in England and Oliver Evans in the United States, changed that. Higher pressure meant more force from a smaller cylinder, so the engine could be shrunk enough to sit on wheels or in a ship's hull.

The railway followed. George and Robert Stephenson's Rocket won the Rainhill trials in 1829, and within two decades Britain was covered by lines. Steamships first worked rivers and coasts, then, with better boilers and the screw propeller, crossed oceans on regular timetables. For the first time in history, people and goods could move overland faster than a horse, and at sea regardless of wind.

Engines kept growing and improving through the century. From a few kilowatts in Newcomen's time and about 20 kW for Watt's engines, the largest stationary and marine engines reached several megawatts by 1900, a thousandfold increase. The best triple-expansion engines, which used the steam three times in successively larger cylinders, reached efficiencies of about 15 to 20%.

Even so, the change was gradual. Water wheels continued to supply much of Britain's industrial power until the 1830s and 1840s, and in the United States water power remained important even longer. As with fuels, prime movers replace each other over decades, not years. Steam also created its own demand for coal and iron. Locomotives, rails, boilers and ships needed vast amounts of both, and the railways in turn carried coal cheaply to every town, so the three industries grew together in a self-reinforcing loop that defined the 19th-century economy.

Data A century and a half of steam engines

| Engine | Date | Typical power | Efficiency |
|---|---|---|---|
| Newcomen atmospheric | 1712 | about 4 kW | about 0.5% |
| Watt with separate condenser | 1770s-1780s | about 20 kW | about 1.5-2.5% (calculated: three to five times Newcomen) |
| Early high-pressure | 1800s | tens of kW | a few per cent |
| Triple-expansion marine | late 1800s | up to several MW | about 15-20% |

 Source: Smil, Energy and Civilization: A History (2017), via Smil Mastery Course, M5 'Coke, iron and the steam engine'  Common misreading

#### Steam did not sweep away water power overnight

Textbooks often show the factory chimney as the instant symbol of industrialisation. In fact, many early mills sat beside rivers because water wheels were cheap and reliable. Steam won because it could be placed anywhere, near workers and markets, and because good river sites ran out. The crossover in British industry took until about the middle of the 19th century.

- Smil, Energy and Civilization: A History (2017) · via Smil Mastery Course, M5 'Coke, iron and the steam engine'
- Smil, Two Prime Movers of Globalization: The History and Impact of Diesel Engines and Gas Turbines (2010) · via Smil Mastery Course, M5 'Coke, iron and the steam engine'

### See it in the table
[H₂O Water](https://www.materialinsights.org/commodities/water/)[Tc Thermal coal](https://www.materialinsights.org/energy/thermal_coal/)[Kc Coking coal](https://www.materialinsights.org/energy/coking_coal/)[S Sulfur](https://www.materialinsights.org/commodities/sulfur/)[Fe Iron ore](https://www.materialinsights.org/commodities/iron_ore/)[St Steel](https://www.materialinsights.org/commodities/steel/)[O2 Oxygen](https://www.materialinsights.org/chemicals/oxygen/)

### Check your understanding

Why was coke needed for iron smelting rather than raw coal?
 Baking coal into coke removes volatiles and gives a strong porous fuel that carries the ore and lets air through.

What was the main waste Watt's separate condenser removed?
 Condensing steam elsewhere let the working cylinder stay hot.

What made locomotives and steamships practical?
 More pressure meant more force from a smaller, lighter cylinder.

[← Part 1: Coal and the great transition](https://www.materialinsights.org/learn/energy/fossil-fuel-revolution/p1/)[Mark read · Part 3: Oil, engines and electricity →](https://www.materialinsights.org/learn/energy/fossil-fuel-revolution/p3/)

## Other sections

- [Module overview](https://www.materialinsights.org/learn/energy/fossil-fuel-revolution/index.md)
- [Coal and the great transition](https://www.materialinsights.org/learn/energy/fossil-fuel-revolution/p1/index.md)
- [Oil, engines and electricity](https://www.materialinsights.org/learn/energy/fossil-fuel-revolution/p3/index.md)
- [The saltation and the century it built](https://www.materialinsights.org/learn/energy/fossil-fuel-revolution/p4/index.md)
- [Fossil-fuelled civilisation today](https://www.materialinsights.org/learn/energy/fossil-fuel-revolution/p5/index.md)
- [Key terms, quiz and sources](https://www.materialinsights.org/learn/energy/fossil-fuel-revolution/review/index.md)