The role of coal in achieving energy sustainability

by John T. McMullan, professor of physics at the University of Ulster

Although oil and gas are getting scarce, there is an abundance of coal left to burn, and the technology to convert it into liquid form is well advanced. Moreover, coal-burning power stations could aid the transition to renewables by providing a market for biomass growers.

As the world's oil and gas production will be limited by resource depletion during the next few decades, we ought to ask if coal is facing the same fate. Will it, too, become costly and scarce in the course of the present century? The answer is a definite no. The world's reserves of coal are very large, and even the present proven reserves are sufficient to meet current global demand for at least 200 years. This is illustrated in Figure 1C1, which also shows the widespread geographical distribution of coal deposits.

(Figure 1C1) Proven World Coal Resources
(at present costs with present technology)
North America120.2137.06257.826.2234
S. & Cent. America7.714.021.82.2381
Europe47.577.9125.412.7 167
Former Soviet Union97.4132.6 230.023.4>500
Africa & Middle East56.
Asia Pacific189.3103.1292.529.7147
TOTAL WORLD519.1465.4984.5100.0216
* 1 Gt - 1 Gigatonn - 1000 million tonnes
** R/P Ratio = Reserves to Production Ratio

If we look further ahead than the known commercial deposits, the picture becomes even more encouraging. It is difficult to obtain accurate figures, but the USA, Australian and Canadian data in Figure 1C2 give a good feeling for the global position. It is clear that the long-term resource is many times greater than the current value of recoverable reserves. Thus, as supplies of coal are plentiful, sufficient for many hundreds of years, it behoves us to consider carefully how this resource should be managed and how it can contribute to the creation of a clean and sustainable future.

(Figure 1C2) Coal resources for USA, Australia and Canada
USA (2001)1(Mtonnes)
Estimated Recoverable Reserves*249,555
Demonstrated Reserve Base**455,913
Confirmed Resource1,550,000
Estimated Resource3,650,000
AUSTRALIA (2001)2(Mtonnes)
Estimated Recoverable Reserves*82,080
Demonstrated Reserve Base**106,760
Confirmed Resourcenot quoted
Estimated Resource430,000
CANADA (2000)3(Mtonnes)
Estimated Recoverable Reserves*6,578
Demonstrated Reserve Base**78,875
Confirmed Resource119,725
Estimated Resource125,100
* viable with today's costs and technology
** viable with a small increase in cost
1. US Geological Survey
2. Australian Geological Survey Office
3. Canadian Geological Survey


Global coal consumption has expanded by about 47% over the last twenty-five years, from 2469 million tonnes in 1976 to 3639 Mtonnes in 2000.

Figure 1C3 shows the distribution of fuel use between the various fuel types. Because of the transport sector and petrochemicals, oil is the largest contributor, but coal is the next largest. One of the strategic advantages of coal is that it is widely distributed, and there are known coal reserves in over 100 countries - most of which are politically stable. Figure 1C4 shows the outputs of the major coal producing countries.

(Figure 1C3) Global Energy Consumption
Global Primary Energy Consumption (1999)
(% by fuel )
Combustible Renewables & Waste11.1%
* Other includes geothermal, solar, wind, heat, etc
(Figure 1C4) Coal Production by Country
Major Producers of Hard Coal
PR China1,171 Mt
USA899 Mt
India310 Mt
Australia238 Mt
South Africa225 Mt
Russia169 Mt
Poland102 Mt
Ukraine81 Mt
Indonesia79 Mt
Kazakhstan71 Mt

If we turn our attention to electricity production, it becomes apparent that coal is the major power generation fuel and is used over twice as extensively as its closest competitor (hydropower). Even more interesting is the extent to which many countries are dependent on coal for electricity production. These aspects are illustrated in Figure 1C5 and 1C6.

(Figure 1C5) Fuels for Power Generation
World Electricity Generation (1999)
(% by fuel)
Other* 1.6%
*Other includes solar, wind, combustible renewables, geothermal & waste
(Figure 1C6) Coal in electricity Generation
Countries Heavily Dependant on Coal (2000)
South Africa90%
PR China80%(e)
Czech Republic71%
EU15 (1999)25%
(e) estimated


Finally, coal is inexpensive and has shown a high degree of price stability over the last two or three decades. This is because of the wide distribution in supplies, the existence of an indigenous supply in most coal-using countries, and the ease and low cost of transporting solid fuel by sea in bulk carriers, and by land on trains.

If global economic growth continues at around the present rate, the world's energy demand is projected to rise by 2 - 3% per annum over the next 25 years. In the electricity sector alone, 3500 GW of new generating plant would be required by 2030 to meet the increased demand. To put this in perspective, the capacities of Ireland's two largest power stations, Poolbeg and Moneypoint, are approximately 1GW and 0.9GW, respectively.

This expansion represents a total global business worth more than €3250 billion (an average of €130 billion per year). Coal-fired plant is expected to account for about 40% of this increase. This will require a coal-based power station investment of over €1300 billion, almost 70% of which will be in Asia. At the moment, about forty power stations are being built per year. Thirty of these are coal fired, and twenty of them are in China. As Europe currently builds over 50% of these power stations, the market over the next 25 years represents potential sales of some €650 billion, to which must be added €150 billion in spares, maintenance and repairs. The heat-only sector (space heating, process steam, iron and steel, cement, etc.) is of similar size, and presents similar opportunities.

Figure 1C7 shows the projection to 2030 for electricity generation demand for the fifteen present member states of the European Union, together with an indication of the amount of capacity that will be less than forty years old at any given time.

It is clear that, over the next thirty years about 500 GW of generation capacity will have to be replaced (that is, about 500 power stations of the size of Poolbeg or Moneypoint will have to be built). This is a major engineering and economic challenge, involving the total replacement of virtually all of the currently operating plant. It presents two problems:

In fact, in view of the necessary plant replacement profiles, renewables and greenhouse gas targets will be very difficult to achieve.

One of the consequences of this new-build requirement, when taken with the supply position of the other fossil fuels, is that coal must continue to play a significant role despite its undoubted environmental difficulties. Thus, it is essential that "clean coal" technologies are developed and deployed so that environmental damage is reduced or eliminated. Most public concern lies with emissions of carbon dioxide because of the greenhouse gas implications and natural gas is widely seen as being preferable because it leads to much lower CO2 emissions per unit of electricity produced.

This raises an interesting point in that, as methane is about 30 times more effective than CO2 as a greenhouse gas, an associated methane leakage of about 1.8% will completely negate the beneficial effects of switching away from coal. The fugitive gas from the US system is estimated to be at least 1.5%, so it would appear that the environmental advantage of using natural gas is more marginal than appears on the surface.

Clean coal technologies aim at reducing the overall emissions resulting from coal utilisation. In general heat production applications, these include

CO2 abatement in such plant concentrates on increasing plant efficiency and improving maintenance and fuel handling so that emissions are minimised. The addition of carbon dioxide capture to most such plant would be prohibitively expensive and complicated.

In the electricity sector, though, there is greater scope for action. The first target is to improve the efficiency of pulverised fuel (PF) plant, the work-horse technology of the industry. When the older plant that is still in use was built in the early 1970s, the state of the art efficiency was about 36% with steam temperatures of about 560oC (see Figure 1C8).

The increasing efficiency of coal-fired power stations as their operating temperatures and pressures rise.

Over the intervening period, this has improved to today's 45% based on supercritical steam plant operating at about 600oC. The immediate target is to achieve 50 - 52% in new ultra-supercritical plant operating at 700oC and very high pressures. This evolution represents a striking 45% increase in efficiency, with corresponding reduction in CO2 emissions. Unfortunately, it is probably very close to the achievable limit because of materials limitations in the face of the aggressive nature of high temperature steam. The implication is, however, that CO2 emissions from conventional coal plant could be reduced significantly by introducing this new technology and could go a long way towards achieving the declared emissions reduction targets.

The introduction of pressurised fluidised bed combustion technology (which would allow the use of gas turbines and combined cycles in coal-fired plant) could, in principle, push this efficiency up to about 55% - representing an improvement of 53% over currently installed equipment.

Ultimately, coal gasification and the use of integrated gasification combined cycles (IGCC) could lead to efficiencies of about 60%, with complete containment of undesirable pollutants within the system, and with the prospect of complete capture and subsequent storage of the CO2. If this target were achieved, it would represent a 66% improvement over present technology, and would exceed the 60% CO2 emissions reduction being mooted as necessary.

Currently, a few full-scale pilot plants are operating around the world, with efficiencies around 45% - useful, but not spectacular. The difficulty with gasification plant is that it is inherently complex and is much more expensive than natural gas combined cycle plant. The equipment in the dashed box in Figure 1C9 is essentially the extra plant that is required.

Until the cost of gas rises to about twice that of coal on an energy basis, commercial pressures will ensure that the natural gas plant will be selected. Currently, the price ratio is about 1.6, so further increases in the price of gas could shift the balance in favour of coal gasification. Other useful coal-based technologies include coal bed methane and underground coal gasification. Coal bed methane (firedamp) is presently being extracted from working and disused pits and used for both power and heat generation. Underground coal gasification provides a route to gasifying the coal in situ and piping the gas to the surface for subsequent use. The advantages of this technique are that it provides access to unmineable coal deposits, greatly increases the amount of coal available for use, and has the potential to leave trace elements, sulphur, etc., buried underground. Several pilot schemes are either in operation or being planned.

The other area where coal has a potentially vital longterm role is in the provision of liquid fuels for transport applications. Essentially, the process is to hydrogenate the coal in a controlled way so that high-grade petrol and diesel are produced. The problems are thermodynamic efficiency and cost - hence there is a need for catalysts to selectively improve the reaction rates.

There are a number of possible processes, some of which have been in large-scale use for over sixty years. For example, Germany depended on coal liquefaction for transport fuels throughout the Second World War, and during its trade boycott, South Africa met all of its petroleum requirements using the SASOL (Synthol) route. The comparative thermodynamic efficiencies and costs of three of the candidate technologies (based on an output of 50,000 bbl/day) are shown in Figure 1C10.

(Figure 1C10) Comparative Performance of Coal Liquefaction Processes
Gasoline/Diesel Yield
(bbl/tonne )
British Coal LSE62.72.711.0
Mobil MTG (Texaco)46.41.991.45
Synthol (Lurgi)38.61.551.67

Interestingly, China has now ordered a plant in Inner Mongolia to produce 50,000 bbl/day of diesel and gasoline using an American direct catalytic reforming process. The plant will cost $2billion, and building is to start in 2003. The fuel cost will be equivalent to a crude oil price of 22-28 $/bbl.


At first sight, coal and renewables (essentially combustible renewables such as biomass and waste) have little in common. However, there are a number of synergetic relations which suggest that coal plant might provide the route by which large scale biomass energy plants could develop.

Essentially, and except in special circumstances, biomass plant is small in scale. The fuel is spread diffusely and must be concentrated and transported to the power plant. This limits the size of the plant to that which matches the locally-available fuel resource. Because of the small size and the low calorific value of the fuel, biomass combustion/gasification is inherently inefficient and suffers large energy losses.

By contrast, coal plant is inherently large in scale and coal has a high calorific value. As a consequence, coal plant is much more efficient and suffers relatively low energy losses. Additionally, coal combustion plant is very flexible and can essentially burn anything. Thus, co-combustion of biomass with coal provides the scale of operation that would allow biomass to be used efficiently. It could also help to solve part of the problem of reducing coalrelated environmental emissions by substituting coal with biomass. If efficient biomass-coal plant were introduced to the Chinese market (efficiency 45%, 10% of fuel biomass-derived), displacing existing plant (average efficiency less than 20%), coal consumption per MWh of electricity sent out would reduce by 60%. This represents a massive potential for reducing global emissions. The scale becomes apparent when it is realised that Chinese coal consumption is about 1200 million tonnes per year (increasing by 100 million tonnes per year), so that the potential saving is over 700 million tonnes of coal per year. By comparison, total European coal consumption is about 160 million tonnes per year.

Moreover, burning coal and biomass together overcomes the uncertainty about what level of distributed small-scale generation can be tolerated on a grid system before instabilities and control problems become a serious problem. The actual levels are unknown, and the implications uncertain. Co-utilisation of coal and biomass provides a route to minimising the problem by using the biomass in larger central coal burning plant and so aiding the maintenance of network stability.

There are a number of other non-technical barriers to the implementation of a renewable energy policy. These include:

The last point illustrates a serious rate-limiting step in the implementation of a biomass programme. The success of any such programme depends critically on the power plant operator having confidence that he will have access to an adequate supply of fuel for a long enough time (typically 15 years) to ensure a return on the capital investment. Simultaneously, the fuel provider must have confidence that there will be a market for his crop to allow his investment to be recouped. The ARBRE experience has seriously damaged this mutual confidence. One solution to this chicken and egg problem could be to use existing or new coal plant to provide the necessary buffer to ensure a flexible biomass market that would allow biomass supply to build up - in turn giving the power plant developers confidence that fuel will be available for the lifetime of their plant.


The quoted data has been taken from publications and the web-sites of World Coal Institute, International Energy Agency, USDOE Energy Information Agency, and the Geological Survey Offices of USA, Australia and Canada.

This is one of almost 50 chapters and articles in the 336-page large format book, Before the Wells Run Dry. Copies of the book are available for £9.95 from Green Books.

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