power generation.
Total recoverable reserves of coal around the world are estimated at 891,531 million tons – the United States has sufficient coal reserves to last (at current rates of consumption) in excess of 250 years (BP, 2019). Even though coal deposits are distributed widely throughout the world, deposits in three countries account for approximately 57% of the world recoverable coal reserves, viz., United States (27%), Russian Federation (18%), and China (13%), and another six countries account for 30% of the total reserves: Australia (9%), India (7%), Ukraine (4%), Kazakhstan (4%), South Africa (3%), and Japan (3%). Coal is also very unequally and unevenly distributed in the world, just as other fossil fuels such as crude oil and natural gas.
Coal has been studied extensively for conversion into gaseous and liquid fuels as well as hydrocarbon feedstocks. Largely thanks to its relative abundance and stable fuel price on the market, coal has been a focal target for synthetic conversion into other forms of fuels, i.e., synfuels. Research and development work on coal conversion has seen peaks (highs) and valleys (lows) due to external factors including the comparative fossil fuel market as well as the international energy outlook of the era. Coal can be gasified, liquefied, pyrolyzed, and co-processed with other fuels including oil, biomass, scrap tires, and municipal solid wastes (Speight, 2008, 2011b, 2011c, 2013a, 2014b). Secondary conversion of coal-derived gas and liquids can generate a wide array of petrochemical products as well as alternative fuels.
For the past two centuries, coal played this important role – providing coal gas for lighting and heating and then electricity generation with the accompanying importance of coal as an essential fuel for steel and cement production, as well as a variety of other industrial activities. On a worldwide basis, in excess of 4 billion tons (4.0 x 109 tons) of coal is consumed by a variety of sectors – including power generation (steam coal and/or lignite), iron and steel production (coking coal), cement manufacturing, and as a solid fuel or a source of liquid fuels (Speight, 2013a, 2103b). In fact, coal remains an important source of energy in many countries, and is used to provide approximately 40% of electricity worldwide, but this does not give the true picture of the use of coal for electricity production. During recent times the coal industry has been pressured into consideration of the environmental aspects of coal use and has responded with a variety of on-stream coal-cleaning and gas-cleaning technologies (Speight 2013a).
Coal is the largest single source of fuel for the generation of electricity worldwide, as well as the largest source of carbon dioxide emissions, which have been implicated as the primary cause of global climate change, although the debate still rages as to the actual cause (or causes) of climate change. Coal is found as successive layers, or seams, sandwiched between strata of sandstone and shale and extracted from the ground by coal mining – either underground coal seams (underground mining) or by open-pit mining (surface mining).
Coal remains in adequate supply and at current rates of recovery and consumption, the world global coal reserves have been variously estimated to have a reserves/production ratio of at least 155 years. However, as with all estimates of resource longevity, coal longevity is subject to the assumed rate of consumption remaining at the current rate of consumption and, moreover, to technological developments that dictate the rate at which the coal can be mined. But most importantly, coal is a fossil fuel and an unclean energy source that will only add to global warming. In fact, the next time electricity is advertised as a clean energy source, just consider the means by which the majority of electricity is produced – almost
1.3.2 Oil Shale
Just like the term oil sand (tar sand in the United States), the term oil shale is a misnomer since the mineral does not contain oil nor is it always shale. The organic material is chiefly kerogen and the shale is usually a relatively hard rock, called marl. Oil shale is a complex and intimate mixture of organic and inorganic materials that vary widely in composition and properties. In general terms, oil shale is a fine-grained sedimentary rock that is rich inorganic matter and yields oil when heated. Some oil shale is genuine shale but others have been misclassified and are actually siltstones, impure limestone, or even impure coal. Oil shale does not contain oil and only produces oil when it is heated to approximately 500oC (approximately 930oF), when some of the organic material is transformed into a distillate similar to crude oil (Lee, 1990; Scouten, 1990; Lee, 1991; Speight, 2008, 2012).
Thus, when properly processed, kerogen can be converted into a substance somewhat similar to crude oil which is often better than the lowest grade of oil produced from conventional oil reservoirs but of lower quality than conventional light oil. Shale oil (retort oil) is the liquid oil condensed from the effluent in oil shale retorting and typically contains appreciable amounts of water and solids, as well as having an irrepressible tendency to form sediments. Oil shale is an inorganic, non-porous sedimentary marlstone rock containing various amounts of solid organic material (known as kerogen) that yields hydrocarbon derivatives, along with non-hydrocarbon derivatives, and a variety of solid products, when subjected to pyrolysis (a treatment that consists of heating the rock at high temperature) (Lee, 1990; Scouten, 1990; Lee, 1991; Speight, 2008, 2012).
Oil production potential from oil shale is measured by a laboratory pyrolysis method called Fischer Assay (Speight, 1994, 2008, 2012) and is reported in barrels per ton (42 US gallons per barrel, approximately 35 Imperial gallons per barrel). Rich oil shale zones can yield more than 40 US gallons per ton, while most shale zones produce 10 to 25 US gallons per ton. Yields of shale oil in excess of 25 US gallons per ton are generally viewed as the most economically attractive, and hence, the most favorable for initial development. Thus, oil shale has, though, a definite potential for meeting energy demand in an environmentally acceptable manner (Lee, 1990; Scouten, 1990; Lee, 1991; Bartis et al., 2005; Andrews, 2006; Speight, 2008; 2012).
The oil shale deposits in the western United States contain approximately 15% w/w organic material (kerogen) (Lee, 1990; Scouten, 1990; Lee, 1991; Speight, 2012). By heating oil shale to high temperatures (>500oC, >930oF), the kerogen is decomposed and converted to a volatile liquid product. However, shale oil is sufficiently different from crude oil and refining processing shale oil presents some unusual problems but, nevertheless, shale oil can be refined into a variety of liquid fuels, gases, and high-value products for the petrochemical industry.
The United States has vast known oil shale resources that could translate into as much as 2.2 trillion barrels of known oil-in-place. Oil shale deposits in the United States are concentrated mainly in the Green River Formation in the states of Colorado, Wyoming and Utah, which account for nearly three-quarters of this potential (Lee, 1990; Scouten, 1990; Lee, 1991; Bartis et al., 2005; Andrews, 2006; Speight, 2008; 2012). Because of the abundance and geographic concentration of the known resource, oil shale has been recognized as a potentially valuable United States energy resource since as early as 1859, the same year Colonel Drake completed his first oil well in Titusville, Pennsylvania (Chapter 1). Early products derived from shale oil included kerosene and lamp oil, paraffin, fuel oil, lubricating oil and grease, naphtha, illuminating gas, and ammonium sulfate fertilizer.
Since the beginning of the 20th century, when the United States Navy converted its ships from coal to fuel oil, and the economy of the United States was transformed by gasoline-fueled automobiles and diesel-fueled trucks and trains, concerns have been raised related to assuring adequate supplies of liquid fuels at affordable prices to meet the growing needs of the nation and its consumers.
