An Introduction to Coal-Fired Power Generation

Coal accounts for around 40% of electricity production globally making it the most important means of power generation in the world and is a major source of carbon dioxide emissions. It has achieved its pre-eminence as a power station fuel because it is cheap and widely available. The fuel has been used as a source of energy for over 4000 years but electricity production from coal only began at the end of the nineteenth century. Initially it was based on steam engines but it advanced with the development of the steam turbine to become the major means of generating electricity during the twentieth century. Many nations have built their prosperity on coal. The largest national users of coal for power generation are China, the USA and India.

Keywords

Coal-fired power generation; steam turbine; coal mining; global electricity production from coal; national electricity production from coal; history of coal-fired power generation

Coal is the most important source of electricity in the world today in terms of the amount of energy it produces. Coal plants provide around 40% of the total electricity generated globally and the proportion of electricity produced by coal-fired power plants has not changed notably over a decade. Moreover the percentage of global power produced by these plants in the second decade of the twenty-first century is marginally higher than it was during the 1970s, though not as high as it was at the middle of the twentieth century.

Coal-fired power generation is important today for a second reason. Coal combustion is one of the main anthropogenic sources of atmospheric carbon dioxide, a major contributor to global warming, and large coal-fired power plants are the most significant single point emitters of the gas. Controlling these emissions can therefore play a major role in controlling the rise in the temperature of the earth’s atmosphere.

Coal has achieved its pre-eminence as an energy source for stationary power generation because it is cheap and it is plentiful. While oil remains the single most important source of global energy because of its versatility, particularly as a transportation fuel, for electricity production coal is king. The fuel is widely dispersed, though it is not found everywhere, and it is cost-effective.

Coal has been burnt to provide heat for close to 4000 years but during the eighteenth century and the Industrial Revolution its use expanded extensively for industrial applications such as smelting and for mechanical power. The modern era rise in atmospheric carbon dioxide concentrations coincides with this period and can be directly linked to the increasing combustion of fossil fuels.

It was towards the end of the nineteenth century that coal began to be utilized for power generation as well as for industrial processes. Since then, most of the world’s richest nations, including the USA, many in Europe, China and India have built their economic foundations on the back of coal. As a consequence this fuel is of strategic importance to many countries and this has made it extremely difficult to displace now that the dangers of global warming have been recognized. Indeed, the use of coal for power generation continues to expand and most realistic scenarios for future energy use suggest this trend is likely to continue well into the middle of the current century.

While coal is relatively cheap to mine, it does not have as high an energy density as either oil or natural gas. This makes it relatively costly to transport, so most coal is used close to the source where it is produced. There is a global market for high-quality coal but it is limited and trade routes are normally as short as possible. Most of the traded coal is used for power generation, particularly in countries such as Japan that have adopted a policy of exploiting a mixture of energy sources to increase energy security but have no coal of their own.

The traditional method of generating electricity from coal is to burn the fuel in a furnace and use the heat generated to raise steam which is then exploited to drive a steam turbine. The technologies utilized in such plants are well established and the best modern plants are capable of achieving an overall energy conversion efficiency of up to 45%. However, many older plants are less efficient than this. An alternative approach to power generation from coal is to convert the solid fuel into a combustible gas and then burn this in a gas turbine. The product of coal gasification can also be used to supply fuel to fuel cells.

Coal contains a very high percentage of carbon so the normal, uncontrolled combustion of coal in air produces large quantities of carbon dioxide which are released into the atmosphere. There are techniques available to capture the carbon dioxide from the waste gases in a coal-fired power plant. Adding carbon capture reduces the overall plant efficiency to around 30% or less, increasing the cost of electricity from such plants. Nevertheless, coal-based generation is potentially still competitive. Political and environmental pressures for change could bring carbon capture technologies to commercial maturity by the third decade of the twenty-first century. However, progress has been slow and that target looks increasingly difficult to meet.

The History of Coal-Fired Power Generation

The earliest established regular use of coal was around 2000 BC in northern and western China, in the region which today covers the Inner Mongolia autonomous region and the province of Shanxi. At that time wood was the fuel most commonly used for heating and cooking in most parts of the world but the availability of wood was scant in this Chinese region while coal was available close to or at the earth’s surface.1 This pattern has been copied in other parts of the world in later eras, with coal used when wood has become scarce. The use of coal in metallurgical processes and metalworking appeared much later. Greek literature cites the use of coal in metalworking at around 300 BC, the first extant reference.

While coal has been used sporadically since those times in many parts of the world, the roots of modern coal use are found in Britain, a country which has a long history of coal exploitation. Coal was mined in Britain by the Romans 2000 years ago. This coal was transported as far afield as the Rhineland where bituminous coal was traded for use in the smelting of iron ore. Coal extraction fell off after Roman influence declined during the fourth century AD and was only revived on any significant scale in the twelfth century. The fuel was used mainly for heating and cooking, replacing wood which was becoming scarce. Metalworking craftsmen, or artificers as they were then known, also took up the use of coal because it burned more hotly than wood or charcoal.

Small-scale use of coal continued into the eighteenth century when the Industrial Revolution stimulated the widespread use of coal both for industrial processes and as a fuel to drive steam engines of various types. Surface mining initially provided most coal but as the eighteenth century progressed, deep mining began to develop. Mining also developed in Germany and Poland during the eighteenth century, and to a small extent in India – then part of the British Empire – but it was not until the nineteenth century that it became widespread elsewhere. At the turn of the twentieth century Britain was still the second-largest coal producer in the world, its production exceeded only by the USA. Ironically Britain, which still has major coal reserves, is now a large importer of coal.

The use of coal for power generation began in the USA in the 1880s, based on the same technology that was then used to create mechanical power, the steam engine. Coal was burned to raise steam and the steam used to drive an engine, which in turn drove a dynamo or alternator which produced electricity. The first fully commercial electric power station was the Pearl Street station in New York which was built by Thomas Edison and started operating in 1882. (An earlier test station was built by Edison at Holborn Viaduct, London, in early 1882 but this station only ran for a few months to prove the technology.) The Pearl Street plant used a Porter Allen reciprocating steam engine and dynamo to produce a direct current which supplied power for lighting. Output was around 130 kW.

The next major advance was the steam turbine which was invented by Charles Parsons in 1884. Steam turbines allowed more efficient energy conversion and higher outputs. By 1900 steam turbines could produce 1200 kW and by 1910 individual units could generate 30,000 kW. These large steam turbines provided the technology on which many of the power stations in the developed world relied (alongside hydropower) and during the twentieth century coal-fired power stations using steam turbines became the most important source of electricity across the globe. They remain the single most important source of electricity in the second decade of the twenty-first century.

Global Electricity Production from Coal

The amount of electricity generated from coal has increased continuously since the beginning of the twentieth century. Early global figures are difficult to find but, in 1949, UN statistics indicate that 531 TWh of electric power was generated from thermal power stations; the majority of these would have been based on coal combustion along with some oil (gas was not yet widely used for power generation). Total global production of electricity in 1949, based on UN data, was 840 TWh, with thermal power plants responsible for 63% of the total, and...