Environmental effects of coal combustion

Uncontrolled coal combustion is a filthy process. It releases a catalogue of unpleasant solids and gases that are potential environmental contaminants. Fortunately various strategies exist, as outlined above, to contain most of these potential pollutants. But even with the most effective pollution-control systems, some environmentally detrimental materials are released.

In many countries the release of the most obvious contaminants such as sulphur dioxide, nitrogen oxides and particulates are controlled by environmental regulations. These may either specify the maximum concentration of pollutant permitted in the flue gas exiting a power station or they may set an upper limit for the total amount of each material that can be released into the environment. In either case, power plant operators will aim to keep within these limits, but only just. Some typical regulation levels are shown in Table 3.2.

Without regulation, all these pollutants cause severe environmental damage. SOX and NOX are responsible for acid rain which has caused widespread damage to forests and lakes throughout the world. Acid rain

Table 3.2 Annual average emission standards (mg/m3)

Sulphur dioxide

Nitrogen oxides


European Union












World Bank





Source: World Bank recommendations, European Union 2001 limits for large power plants, World Bank Technical Paper No. 286.

Source: World Bank recommendations, European Union 2001 limits for large power plants, World Bank Technical Paper No. 286.

can also cause damage to stonework as may be seen from the Taj Mahal to the centre of London. NO* help cause smog, as do the ash particles released from a power plant. All these pollutants can cause health problems when inhaled and their effects are compounded when significant amounts of trace metals such as mercury, lead or cadmium are also released.

More serious perhaps, certainly potentially more far-reaching in its effects, is the threat of global warming as a result of the release of excessive quantities of carbon dioxide into the atmosphere. Carbon dioxide is one of a number of gases (methane and SO2 are others) which have been implicated in the greenhouse effect. These gases allow heat from the sun to reach the surface of the earth but then prevent it from being re-radiated into space. The effect is to raise the average global temperature (see Chapter 2).

So far the control of carbon dioxide emissions has been left to the broad targets set by the Kyoto agreement. These aim, as a first step, to return the rate of emission of carbon dioxide to levels around 6-8% below those seen in 1990 by between 2008 and 2012. (These targets only apply to the industrialised nations. Developing nations are broadly exempt though they will be embraced by the treaty at a later date.) This target is being achieved, without much effort in some cases, by a switch to the combustion of natural gas rather than coal or oil and by the steady increase in the efficiency of modern power plants. A downturn in the global economy at the end of the twentieth century has also had a beneficial effect.

This is a short-term measure. In the long term it will be necessary to legislate to introduce the technology to capture and store carbon dioxide. Such legislation will have a significant effect on the economics of coal-fired power plants. However the time scale for the introduction of such measures is far from clear and the resistance from the interested parties is intense.

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