Battle in Print: Waking Up to Coal

Dave O'Toole, 26 October 2006

In suggesting that we cycle and recycle, save on the odd polythene bag, and forgo our holidays abroad, there are many environmentalists who – whilst concerned about the effects of carbon production on global warming – do not consider the real state of energy production worldwide. A debate is ongoing about the merits of nuclear power, which ignores the fact that we already have nuclear power generation involving 442 power stations in 32 countries.[1] There is an existing economy already dependant on oil, with powerful vested interests, and despite dire warnings in the past about oil running out this is not about to happen any time soon.

One of the salient facts which tends to be ignored is that coal, that most undesirable of energy sources, plays a vital role in world power and this role is set to continue. Coal currently fuels 39 per cent of the world’s electricity production and this proportion is expected to remain at similar levels over the next 30 years. As an IT consultant faced many times with an overenthusiastic client who wanted design systems as a ‘green field site’ I found myself retelling the same joke. It concerns an Irishman who, when asked for directions to Dublin, frustratingly gives first one set of unfinished instructions followed by another, again unfinished, alternative route. Finally, he looks around at the scenery and, noting his location, says: ‘Sure, if I were you, I wouldn’t be starting from here’.

If we are to accept that global warming is caused by human activity (production of greenhouse gases) we must accept that we must ‘start from here’. Consumption of steam coal is projected to grow by 1.5 per cent per year over the period 2002-2030 and Lignite, also used in power generation, will grow by 1 per cent per year. Demand for coking coal in iron and steel production is set to increase by 0.9 per cent per year over this period.[2]

The top hard coal consumers are China, USA, India and Japan with 2000, 900, 400 and 200 million tonnes respectively. The biggest market for coal is undoubtedly Asia, which currently accounts for 58 per cent of global hard coal consumption. China is responsible for a significant proportion of this.

Coal will continue to play a key role in the world’s energy mix, with demand in certain regions set to grow rapidly. Growth in both the steam and coking coal markets will be strongest in developing Asian countries, where demand for electricity and the need for steel in construction, car production, and demands for household appliances will increase as incomes rise. Nor can we reasonably deny these Asian countries the ability to develop their economies. Whereas the UK and US ranked tenth and fourth in terms of Gross National Income in 2004, China and India ranked 22nd and 129th respectively.[3] Coal supplies two thirds of China’s primary energy, compared with less than a quarter for the US. As China has four times the population of the US, we can easily see that China is heavily dependant on coal for its development.[4] The prospects for limiting the growth of production of greenhouse gases, in particular carbon dioxide, seem grim when we consider this.

Coal is at first sight a very unattractive energy source. It is inconvenient to extract, transport, store and use when compared with gas or oil. It can produce up to twice the amount of carbon dioxide for the same useful heat. A large coal-fired power station can produce enough ash in a year to cover an acre of ground to the height of a six storey building. Potentially, its flue gases can carry several tonnes of sulphur dioxides and nitrous oxides into the atmosphere per day. Energy from coal production in 2000 is three times what it was in 1920, but as a fraction of all forms of energy it has fallen from over four fifths to less than a quarter, due, no doubt, to the attractions of other energy sources (Boyle et al 2003). However, whilst it may be an undesirable fuel, it has one overriding advantage: there is a great deal of it.

There are known coal reserves of 745,000 million tonnes with annual world consumption running at 3280 million tonnes. This is a conservative 227 years worth of known reserves (Boyle et al 2003: 167). Fortunately, the coal industry has moved on from the time of the Industrial Revolution. Many of the unattractive features of coal are due to its complex chemical makeup. It is by no means a homogeneous product. Its main constituents, as with all fossil fuels, are carbon and hydrogen; but coal, unlike gas or oil, cannot be analyzed at the molecular level into straightforward hydrocarbon compounds. Coal compounds incorporate complex, layered molecular arrangements which incorporate not only carbon and hydrogen but also oxygen and nitrates. The structure includes different quantities of sulphur, as well as inert material destined to remain as ash. In addition, all coal contains moisture which makes it less suitable for burning.

A better understanding of the chemistry of coal allows for a more sophisticated approach to its ultimate use. There are many of these. Coal may ignite with difficulty or relative ease, be suitable for power stations or for the production of coke. It has a myriad of possible uses and qualities, including the production of coke, gas, oil and complex chemicals. There are also many options for burning coal which are aided by a better understanding its composition. These are listed below:

Grate Boilers

Fuel is crushed to only a few millimetres across and fed by conveyor belt across a grate through a pressurised upward flow of air. Fixed carbon burns on the grate and volatile matter (oils and gases) in the space above. Boilers of this type can use the cheapest forms of coal supplemented by bio-fuels.

Pulverised Fuel Boilers

Pulverised fuel less than 100 microns (0.1 mm) in diameter is fed into the boiler. The dust is so fine that it floats in a controlled jet of air through the burner jets. The fixed carbon burns completely in a very short time so that the volatile products are quickly released and burn with the fixed products in the same part of the furnace. This raises the temperature of the burn and increases the efficiency of heat transfer. The quick burn results in reduced quantities of nitrous oxide compounds.

Fluidized Bed Boilers

Fluidized Bed Combustion (FBC) can be used to burn coal but has the additional benefit that a variety of materials such as household waste may be incorporated into the ‘burn’. In an FBC plant a thick layer of sand or gravel lies on a base plate that has many small apertures through which high pressure jets of air are blown. The mass of material expands to the depth of about a metre and begins to take on the physical properties of a liquid. Objects placed in it will sink or float as if in a liquid. Fuel particles placed into this will burn in a plentiful supply of oxygen whilst maintaining good physical separation. Fixed carbon and volatile products again burn together, resulting in good heat transfer to water-carrying tubes.

Circulating Fluidized Bed Combustion (CFBC)

In this system an increased air flow drives some of the particles into the space above the fluidized bed where they act more like a hot gas. This circulation of particles from the bed to the air space above allows for better, lengthier combustion, allowing a wider range of coal types – and other fuels – to be used.

Gas from Coal

By heating coal in the absence of air, coke can be produced in the same way as charcoal is produced from wood. This product is the reducing agent used in the production of iron and steel, but can also be burned more cleanly that can coal. A by-product of this process is coal gas, which can also be burned. Gas, of course, has advantages over coal in that it can be delivered through pipes.

Oil from Coal

Crude oil chemically has a higher hydrogen composition than does coal. It is therefore necessary to add hydrogen (or remove carbon) to convert it to useful hydrocarbon products. During the apartheid period in South Africa oil was routinely produced from coal whilst the country operated under a siege economy.

Of course the principal arguments against coal lie in the problems of CO2 emissions, but these problems are not insurmountable. A few examples are given below:

Carbon Sequestration in Forests

When trees grow they take carbon dioxide from the atmosphere. Despite the fact that afforestation of an area of land the size of Europe would be necessary to sequester the carbon which would be produced during the first half of the twenty-first century, it is unlikely that this would be suggested as the sole method of sequestering. Such trees could additionally be themselves used as bio fuels, reducing reliance on the original fossil fuels.

Carbon Capture and Sequestration beneath the Earth’s Surface

In this approach, CO2 is captured from flue gases and deposited beneath the earth’s surface. Depleted oil or gas wells, deep coal seams and aquifers may be possible candidates for use in this way. Captured CO2 can, in fact, be useful when injected into oil wells as this can result in enhanced oil recovery. The pressure of the gas is used to push additional oil to the surface. The extra oil recovered has a value greater than the cost of pumping in CO2.

One possible location to sequester CO2 is in coal seams too deep to be accessible to mining. Such seams often hold considerable quantities of methane, itself a fuel. Again, the economics are such that the value of methane recovered is greater that the cost of pumping in CO2.

Ocean Sequestration

The oceans are already the greatest stores of CO2, however produced. The surface of the ocean is already saturated with CO2, yet the ocean depths have huge CO2 carrying capacity. It has been estimated that if the entire fossil fuel reserves were burned and the CO2 sequestered in this way the CO2 content of the seas would rise by only 17 per cent and there are many more possible strategies for oceanic sequestration other than the simple solution outlined.

The shortages of oil and gas predicted in the 1970s have not materialised. Known reserves, though considerable, will not make oil and gas as long-lived as coal. As far as we can tell, this least desirable of fossil fuels will remain, for some time at least, the one that is in greatest supply. Coal, though, can be converted into more acceptable forms. It is a rich source of hydrocarbons, and thus valuable organic compounds can be synthesised from it. It can currently be burned in acceptable ways with low production of pollutants. It can, in fact, be burned alongside household rubbish in fluidised bed systems lessening pressure on land-fill sites.

There are many possible strategies available for carbon sequestration which will allow us to address the suggested problems posed by greenhouse gas emissions. It seems that the choices open to us by the middle of this century will be down to coal and nuclear. Given that we cannot hold back development of the two of the most populace countries in the world (China and India) with the greatest reserves and the greatest need to develop, the sooner we wake up to the facts of coal the better.

Dave O’Toole is a lecturer in computing, Newcastle College and has a degree in Business Studies

 Footnotes

[1] See the European Nuclear Society website: http://www.euronuclear.org/info/encyclopedia/n/nuclear-power-plant-world-wide.htm

[2] See the World Coal Institute website: http://www.worldcoal.org/pages/content/index.asp?PageID=104

[3 ] Note that this is for per capita income. See: http://www.finfacts.com/biz10/globalworldincomepercapita.htm

[4] See the Carbon Sequestration Forum website: http://www.cslforum.org/china.htm

 References

Boyle, G., B. Everett & J. Ramage (2003). Energy Systems and Sustainability. Oxford, Oxford University Press.

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