Coal, Consumption of
Coal, Consumption of
COAL, CONSUMPTION OF
INTRODUCTION AND BACKGROUND
Coal, essentially fossilized plant material, has been used as an energy source for centuries. As early plants decomposed in the absence of oxygen (for example, at the bottom of deep lakes), oxygen and hydrogen atoms broke off the long organic molecules in the plant material, leaving mostly atoms of carbon, with some other impurities. Formed as long as ago as 300 million years and more, during the Carboniferous Period (named for obvious reasons), coal's main useful component is carbon.
Coal comes in various forms. Older coal is harder, higher in energy content and has a higher proportion of carbon. Anthracite is the hardest, purest version, with a carbon content of about 90 percent. It is also rarer, found in the United States almost exclusively in eastern Pennsylvania. Its energy content is about 25 million Btus per short ton, 67 percent higher than lignite, the softest form of coal, which sometimes contains less than 40 percent of carbon (most of the balance being water and ash—the latter composed mostly of sodium carbonate and potassium carbonate). Lignite is much younger than anthracite. Some lignite deposits are less than 100 million years old (a third the age of most anthracite), being formed from plants that lived in the Cretaceous and Tertiary Eras. Not all of its impurities, in the form of water, carbonates, or independent atoms of oxygen and hydrogen have had the time to be removed by geological and chemical processes.
Bituminous coal—an intermediate form—is and by far the most widely found and used. Its energy content averages around 21.5 million Btus per short ton. Some forms of coal have a substantial sulfur content and contain other impurities as well, chiefly carbonates. Peat, also used as an energy source through burning, can be viewed as an earlier stage of coal: pressure in the absence of oxygen over a period of tens of millions of years will change peat into coal.
The oxidation of carbon through burning produces a significant amount of heat through an exothermic reaction, a chemical reaction that releases energy. However, since most of the energy gained from burning coal results in the production of carbon dioxide (CO2), this principal greenhouse emission is higher for coal than for other fossil fuels, namely oil and natural gas, in which other elements are oxidized in addition to carbon. Because the burning of coal produces so much carbon dioxide, its use will be severely affected by compliance with the Kyoto Protocol, discussed in a following section.
The other fuels, when burned, also produce water vapor and—in the case of oil—other hydrocarbons, as well as carbon dioxide. For equal amounts of energy, oil produces about 80 percent of the CO2 that coal does; natural gas only produces 55 percent of coal's CO2 level.
EARLY HISTORY OF COAL USE
According to the U.S. Energy Information Administration, although scattered use of coal may have occurred as early as 1100 b.c.e., it was substantially later before coal became widely used. Nevertheless, coal has been utilized for millenia. In China, as early as the fourth century c.e., coal sometimes substituted for charcoal in iron smelting. By the eleventh century, coal had become the most important fuel in China, according to The Columbia History of the World(Garrity and Gay, 1972). In the Middle Ages, in various parts of Europe, especially England, coal began to be used as an energy source for smelting, forges, and other limited applications. But it was not until the fifteenth century that it began to be used for residential heating.
England's good fortune in having large deposits of coal was particularly important for that nation, as the English had destroyed most of their forests between the twelfth and sixteenth centuries, in order to produce heat (chiefly residential), as well as charcoal for industrial purposes. By 1840, Britain's coal production was ten times that of Prussia and significantly higher than that of France and other European nations. The availability of coal, along with various inventions, such as the Watt steam engine, which was usually coal-driven, helped the Industrial Revolution to begin in Britain in the last quarter of the eighteenth century. The rest of Europe began catching up a few decades later. But still, around 1870, Britain alone produced over 30 percent of the manufactured goods in the world.
Coal is used to produce coke, manufactured by heating coal in the absence of air. Coke, when heated to high temperatures, yields carbon monoxide, which reduces the iron oxides in ore to iron. Steel contains a small quantity of carbon in an alloy with iron, and coke refining adds carbon to the iron, in addition to refining the ore. As a result of their supply of coal, the British had the capacity to smelt considerably more iron and later, steel, than other countries, resulting in military and economic advantages.
With the development of improvements in the steam engine and other inventions useful for manufacturing—often in the area of textiles—the British were also able to expand new, energy-intensive industries more rapidly than their competitors. At the beginning of the nineteenth century, switching from renewable (animal, wind, hydroelectricity, and mainly wood) energy resources to coal became the hallmark of strong, expanding economies.
HEALTH EFFECTS OF COAL COMBUSTION
Some effects of massive coal burning are quite pernicious, particularly in the absence of strong efforts to reduce the sulfates and other pollutant byproducts. The London "pea soup" fog, conjuring up mystery, intrigue, and respiratory disease, was largely due to the intensive use of coal in conjunction with stagnant and humid meteorological conditions. This local weather effect has virtually vanished in London since the advent of centrally generated electricity as a substitute for coal fires in each individual living area. Much of this electricity is now fueled by nuclear energy among other sources. Another mitigating factor has been the introduction of anti-pollution measures at coal-burning plants, including limestone scrubbers in smokestacks and fluidized bed reactors for coal combustion.
While it was prevalent, the persistent presence of coal-generated smog was found to have serious health effects on the public. This became apparent on days when air pollution was especially bad, and hospital admissions for respiratory ailments increased considerably. The classic example is the "Great London Smog" of December 4, 1952, to which was attributed a net increase of about 4,000 deaths in the following several days. More recently, in Czechoslovakia and East Germany, following the close of the Cold War, researchers discovered that in several severely impacted locations, the rate of upper respiratory disorders—especially among children—was extremely high.
REDUCED COAL EMISSIONS THROUGH TECHNOLOGICAL ADVANCES
Over the past decades, advances have been made that reduce environmental impacts of coal burning in large plants. Some are standard and others experimental. Limestone (mainly calcium carbonate) scrubber smokestacks react with the emitted sulfates from the combustion and contain the chemical products, thereby reducing the release of SOx into the atmosphere by a large factor (of ten or more). Pulverization of coal can also allow for the mechanical separation of some sulfur impurities, notably those in the form of pyrites, prior to combustion. Currently deployed—with more advanced versions in the development stage—are various types of fluidized bed reactors, which use coal fuel in a pulverized form, mixed with pulverized limestone or dolomite in a high temperature furnace. This technique reduces sulfate release considerably. There are pressurized and atmospheric pressure versions of the fluidized bed.
Each technique has its own advantages, but the pressurized version, operating at high temperature, also makes use of jets of the combustion gases to keep the pulverized fuel/limestone mixture in a suspension, later employing both waste heat and a turbine, driven by a jet of combustion gases, to extract more of the energy generated by the reaction. Design engineers hope to increase efficiencies from the standard level of about 33 percent to 40 percent and even, possibly, approaching 50 percent. If successful, this increase in efficiency could have a major positive impact on carbon dioxide emissions, since up to 50 percent more energy could be extracted from the same amount of oxidized coal. Thus, these technologies, while greatly reducing sulfate emissions, can contribute to reducing carbon dioxide emissions by increases in efficiency.
Nevertheless, in the minds of much of the public and of decision–makers, there is a preference for substituting coal with natural gas (which is primarily methane, CH4) to the degree that is easily feasible. Natural gas produces far less of most types of pollutants, including SOx, NOx, and CO2. The tendency away from coal is mitigated by the fact that coal is much cheaper as a fuel (although the capital cost of building a coal plant is higher). For electricity plants that are already built and whose capital costs are sunk, coal's advantage is clear: it costs $0.85 per million Btu, compared with $2.18 per million Btu for natural gas and $2.97 per million Btu for crude oil.
U.S. COAL CONSUMPTION: QUANTITATIVE EVOLUTION
Throughout the industrialized world over the past two centuries, coal became relied upon as an energy source for industrial processes and for residential heat. In the United States, all the coal consumed before the year 1800—much of it imported from Britain—amounted to only 108,000 tons, which is one ten-thousandth of current annual U.S. production. Until 1840, wood exceeded coal as an energy source. However, coal then began a slow, steady expansion in usage, and, for over a century, until 1951, it was the chief energy source in the United States, contributing in the area of transportation (railroads) as well as the earlier, familiar sectors of industrial processes and residential heat.
With the discovery of oil in Pennsylvania in 1859, the seeds of a new energy era were sown. After an initial period of growth from a zero base, oil began to contribute significantly to the energy budget around the turn of the century. In the years following, oil slowly substituted for coal in transportation, starting with automobiles (where coal-fired steam engines had never been very successful) and continuing in trains. Later, it also displaced coal in residential heat and many industrial processes as well as, to a degree, in electricity generation. The "cleaner" energy sources that smelled better than coal began to be substituted for it, particularly in the post–World War II period. From 1952 to 1983, coal lost its primary position, and oil and natural gas vied for the title of main energy source in the United States (oil always remained ahead). But since 1984, coal has regained the lead in domestic production, although not consumption, due mainly to its renewed leading role in electricity generation. The development of cleaner combustion methods
removed some of the political objections to obvious coal pollution, in the form of sulfates and particulates. These methods could be introduced economically, due to the advantages of scale inherent in the centralized nature of electricity production.
Since coal consumption bottomed out in the 1960s, there has been a steady increase in the fraction of energy produced by coal in the United States. About 90 percent of coal use in 1996 was for electricity generation, and most of the rest of its usage was accounted for in industrial coking processes. Nuclear power had a chance to substitute for coal in electricity generation and, to an extent, made serious inroads until encountering significant political and economic problems related to perceptions of public safety and to the increasing cost of nuclear facilities. Following the Three Mile Island nuclear accident in 1979, the use of nuclear power as an energy source was strongly opposed by many public interest groups. No new plants in the United States that were ordered after 1973 have been completed. Thus, it is unlikely that the United States will see widespread replacement of coal–fired electric plants by the nuclear option for the foreseeable future.
The Organization of Petroleum Exporting Countries (OPEC) oil embargo in 1973 resulted in temporary oil shortages in the United States. This crisis focused attention on the need to minimize oil's use except for transportation, for which no other energy source would provide a very effective substitute. As a result, coal use has increased in both fractional and absolute terms since the 1970s and now is the single largest domestically produced energy source in the United States. In 1996, some 21 quads of energy were produced by coal, and in 1997, coal energy consumption rose to 23 quads. About one-third (31%) of all domestic energy production in the United States now comes from coal, which also produced a majority (52%) of the nation's electricity in 1997. Coal accounted for over one–quarter of energy consumption, since a large amount of petroleum is imported from other countries. In addition, nearly 10 percent of U.S. coal production is exported. Table 1 shows the trends in energy consumption by source in the United States.
WORLD COAL CONSUMPTION
The recent history of the world use of coal roughly follows that of the United States for two reasons. First, the United States and the industrial nations have had, in the aggregate, similar energy behavior in terms of energy sources. Second, the United States itself accounts for about one quarter of world energy use. Thus, world energy use patterns reflect, to a considerable degree, those of the United States.
World coal usage, inclusive of the three major types of coal—anthracite, bituminous (by far the most prevalent form) and lignite—reached a plateau in the first decade of the twentieth century and climbed only very slowly in the half century that followed. By 1880, coal use had equaled wood use on a worldwide basis. The usage around the turn of the century was on the order of 2.2 gigatons per year (around 55 quads), of which about 600 million tons were in the United States. World oil production progressively supplemented the use of coal between 1900 and 1950, increasing by more than an order of magnitude in that period of time, from a little over a quad to some 20 quads. Coal's increase over those years was fractionally much less.
After 1930, four other energy sources began to contribute significantly, as wood use continued its slow decline and coal production was relatively flat. These four were oil, natural gas, nuclear power (beginning in the 1950s), and hydroelectricity. The
latter two are relatively small players, but oil and natural gas are major sources of energy, with oil energy production actually exceeding coal in the 1960s.
The first oil crisis in 1973 was a politically–driven event. It resulted from production cutbacks by oil–producing nations following the Yom Kippur War between Egypt and Israel and marked a watershed in patterns of energy use in the industrialized world—especially, as previously noted, in the United States. Oil was saved for transportation to the degree possible, when it became evident that there would be an increased reliance on potentially unreliable foreign sources as domestic sources were depleted. Energy conservation achieved a strong boost from this traumatic event, in which oil prices rose sharply and the uncertainty of oil sources became clear to First World nations.
Since the early 1990s the United States has imported more oil than it has produced for its own use. And, as the nuclear option became frozen, coal has become the chief source for generating electricity, which itself accounts for about 35 percent of the energy sector. In 1997, 52 percent of electricity produced in the United States was generated from coal and in other recent years the fraction has approached 56 percent. Since the United States accounts for one–quarter of total world energy usage, the increase in coal use in the United States alone has a significant impact on worldwide statistics.
EFFECTS OF THE KYOTO PROTOCOL
The U.S. Department of Energy (DOE) has analyzed and projected energy use by sector and energy source for a number of years. One recent forecast (see Table 2) analyzed the implications of the international agreement in the Kyoto Protocol to the United Nations Framework Convention on Climate Change. The United States committed, under the Protocol (Annex B), to reduce greenhouse emissions by 7 percent from 1990 levels by the period between 2008 and 2012. This translated to a 31 percent decline in the production of greenhouse gases (chiefly carbon dioxide) relative to the DOE's assessment of the most likely baseline number, for U.S. energy use and related carbon dioxide emissions predicted for that time.
Other industrial states have committed to reductions nearly as large. However, the world's chief user of coal, China, as a developing nation, has not yet made solid commitments to reduction. Neither has India, another major coal burner, although it uses less than one-quarter as much as China. Limitations on emissions by these emerging world powers are still the subject of discussion. It is clear that, without some limitations on CO2 emissions by major Third World industrializing nations, the goal of rolling back world greenhouse emissions to the 1990 level will be very difficult to achieve.
In 1995, about 92 quads of coal-fired energy were consumed in the world. This constituted close to one-quarter of the 366 quads estimated to be the world's total energy production. The level of coal use will be a major determining factor in whether greenhouse emission goals for 2010 will be met. Assessing the likely state of affairs for coal use at that time requires predicting the state of the world's economies by region as well as estimating probable technological advances by then.
By the year 2010, one DOE model predicts a world energy level of 520 quads per year. Countries already using relatively large quantities of energy will contribute less to the increase in the total energy use than will large, rapidly developing countries, such as China. The projected U.S. excess of carbon dioxide release over that permitted by the Protocol will be on the order of 550 million tons of carbon per year (1803 million metric tons, rather than 1252). Of course, this projected excess would arise from all fossil fuel use, not just that of coal. However, for comparison, in coal equivalent energy, this amounts to some 700 million tons, or about 20 quads, which amounts to 18 percent of the total projected energy use for the United States in that year. It would come to nearly 90 percent of current coal consumption.
Looking at the allocation of energy production among sources, the Kyoto Protocol is meant to increase preference for those energy sources that do not produce carbon dioxide and, secondarily, for those that produce much less than others. There will be a particular disincentive to use coal, since this source produces the most CO2 per energy produced.
The most likely substitute for coal is natural gas, which, as noted earlier, releases about 55 percent of the amount of carbon dioxide that coal, on the average, does. In addition, it produces far fewer other pollutants, such as sulfates and polycyclic hydrocarbons, than coal and oil yield on combustion.
Current U.S. coal consumption is just under 1 billion short tons per year—second highest in the world—after China, which produces some 50 percent more. By 2010, the projected U.S. baseline energy case (in the absence of any attempt to meet Kyoto Protocol limits) would raise this level to 1.25 billion tons, in rough numbers. Coal currently accounts for about one-third of all United States carbon dioxide emissions. If the same patterns of energy source use were to hold in 2010—and if one wished to reduce the carbon dioxide emissions by 30 percent, while making no reductions in usage of other fossil fuels—this would mean reducing coal emissions by 90 percent. Such a scenario is clearly highly unlikely, even if one were to take much longer than 2010 to accomplish this goal.
Moreover, substituting 90 percent of coal with natural gas would reduce the level of emissions only by 0.90 × 0.45 = 0.38, which is still less than half way to the goal of reducing emissions by an amount equal to that produced by 90 percent of U.S. coal use.
Therefore, merely reducing coal use will not be sufficient to satisfy the Protocol. Any plan to comply with the Protocol needs to assume substitution, first by non-combustion energy sources—that is by renewables or nuclear energy—and second by natural gas. This would have to be accompanied by achievement of far greater efficiencies in energy production (for example by introduction of far more fuel-efficient steam gas turbines, driven by natural gas) and by more efficient use of energy.
The remaining possibility for the United States, under the Kyoto Protocol, would be to compensate for the excess of carbon emissions over the committed goal by either planting more trees, in the United States or elsewhere, or by purchasing carbon "pollution rights," as envisioned by the protocol, from other countries. How either of these schemes will work out is in some question. Both would require bilateral agreements with other countries, probably many other countries. The template of the trade in acid rain "pollution rights" to help all parties meet agreed–upon goals may not be a good analogy for carbon emissions, since acid rain, although international, is generally a regional, not a global problem. Further, carbon sources and sinks are not as well understood as are the sulfate and nitrate sources (chiefly coal) that are responsible for acid rain. This uncertainty will make it more difficult to achieve the international agreements necessary to make the "pollution trade" work as a widely-accepted convention, necessary due to the global nature of the problem.
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