Coal-Fired Power Generation Handbook. James G. Speight

can be maintained at a competitive level and the environmental issues can be addressed successfully, there is a future for coal – a long future and a bright future.

      Finally, the issues logic of distinguishing between resources (which include which include additional amounts of coal such as inferred/assumed/speculative reserves) and proven reserves (which are defined as being proved) is that over time production and exploration activities allow resources to be reclassified into proven reserves.

1.6 Reserves

      The coal reserves and resources of the world are difficult to assess because of the lack of accurate data for individual countries. Two fundamental problems make these estimates difficult and subjective. The first problem concerns differences in the definition of terms such as proven reserves (generally only those quantities that are recoverable) and geological resources (generally the total amount of coal present, whether or not recoverable at present).

      Thus, in any text dealing with coal, there must be recognition, and definition, of the terminology used to describe the amounts, or reserves of coal available for recovery and processing. But the terminology used to describe coal (and for that matter any fossil fuel or mineral) resource is often difficult to define with any degree of precision (Speight, 2011b, 2014, 2020).

      Different classification schemes (Chapter 2) often use different words which should, in theory, mean the same but there will always be some difference in the way in which the terms can be interpreted. It might even be wondered that if the words themselves leave much latitude in the manner of their interpretation, how the resource base can be determined with any precision. The terminology used here is that more commonly found although other systems do exist and should be treated with caution in the interpretation.

Generally, when estimates of coal supply are developed, there must be a line of demarcation between coal reserves and resources. Reserves are coal deposits that can be mined economically with existing technology, or current equipment and methods. Resources are an estimate of the total coal deposits, regardless of whether the deposits are commercially accessible. For example, world coal reserves were estimated to be in excess of one trillion tons (1 x 10¹² tons) and world coal resources were estimated to approximately 10 trillion tons (10 x 10¹² tons) and are geographically distributed in Europe, including all of Russia and the other countries that made up the former Soviet Union, North America, Asia, Australia, Africa, and South America (Table 1.7).

      However, there are definitions that go beyond reserves and resources. To begin at the beginning, the energy resources of the Earth are subdivided into a variety of categories (Figure 1.4) and the resources of coal (as well as each of the other fossil fuel resources) can be further subdivided into different categories (Figure 1.5) (Speight, 2013, 2014, 2020).

      1.6.1 Proven Reserves

The proven reserves for any commodity should provide a reasonably accurate estimate of the amount that can be recovered under existing operating and economic conditions. To be economically mineable, a coal seam (coalbed, also called a coalbed, hence coal bed methane) bed must have a minimum thickness (approximately 2 feet) and be buried less than some maximum depth (approximately 6,600 feet) below the surface of the Earth. These values of thickness and depth are not fixed but change with criteria such as (i) coal quality, (ii) coal demand, (iii) the ease with which overlying rocks can be removed for surface mining or a shaft sunk to reach the coal seam for underground mining. The development of new mining techniques may increase the amount of coal that can be extracted relative to the amount that cannot be removed. For example, in underground mining, which accounts for approximately 60% w/w of world coal production, conventional mining (pillar mining) methods leave behind large pillars of coal to support the overlying rocks and recover only about half of the coal present. On the other hand, longwall mining, in which the equipment removes continuous parallel bands of coal, may recover almost all the coal present in the seam.

Table 1.7 Estimated Coal Reserves by Country (Energy information Administration, 2011).

Coal
United States	27.5%
Russia	18.3%
1. China	13.3%
Other Non-OECD Europe and Eurasia	10.7%
Australia and New Zealand	8.9%
India	7.0%
OECD Europe	6.5%
Africa	3.7%
Other Central and South America	0.9%
Rest of World	3.2%
Total	100.0%

      Source: US Energy Information Administration, International Energy Outlook, September 2011.

      Figure 1.4 Energy Resources of the Earth (Speight, 2013).

      Figure 1.5 Resource and reserve terminology (Speight, 2013).

      In addition, an issue which concerns the estimation of reserves, is the rate at which the coal is consumed. When considering the worldwide reserves of coal, the number of years that coal will be available may be more important than the total amount of coal resources. For example, the coal reserves may be estimated using the current rates of consumption, which may indicate that the world coal reserves should last more than 300 to 500 years. However, a large amount of additional coal is present in Earth but cannot be recovered using current technology and these resources, sometimes called geologic resources, are even more difficult to estimate, but may be much greater than the amount of proven reserves.

      Thus, in the current context, the proven reserves (proved reserves) are those coal reserves that are actually found (proven), usually by drilling and coring. The estimates have a high degree of accuracy and are frequently updated as the mining operations proceed. However, even though the coal reserves may be proven, there is also the need to define the resources on the basis of what further amount of coal might be recoverable (using currently available mining technology without assuming, often with a very high degree of optimism) extravagantly, that new technology will miraculously appear or will be invented) and non-recoverable coal reserves will suddenly become recoverable.

      If economic aspects are not considered, the term for the total technologically extractable amount of coal is the producible fraction, which is often confused with the proven reserves. The term proven reserves is further subdivided into proved developed reserves and proved undeveloped reserves. This should not be confused with unproven reserves, which are broken down into probable reserves and possible reserves – those reserves that only have a 10% likelihood of being recoverable.

These